Document:

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                                                                    EXHIBIT 10.5

                              AMENDED AND RESTATED
                              --------------------
                               DEED OF TRUST NOTE
                               ------------------

$15,500,000.00                                                 As of May 7, 2004

     THIS AMENDED AND RESTATED DEED OF TRUST NOTE is made and entered into as of
the 7th day of May, 2004, by and between ARGO ORCHARD RIDGE, LC, a Maryland
limited liability company ("Argo") and FOULGER LAND LIMITED PARTNERSHIP, a
                            ----
Virginia limited partnership ("Foulger", Argo.and Fougler herein referred to
                               -------
individually and collectively as "Maker") jointly and severally, and UBS REAL
                                  -----
ESTATE INVESTMENTS INC., a Delaware corporation ("Payee").
                                                  -----

                             PRELIMINARY STATEMENTS

     A. A loan was made to Maker in the original principal amount of ELEVEN
MILLION THREE HUNDRED NINETY THOUSAND AND NO/100 DOLLARS ($11,390,000.00), the
repayment of which is evidenced by a Promissory Note dated September 28, 2000
(the "Original Note").
      -------------

     B. The Original Note is secured by a Deed of Trust, Assignment and Security
Agreement dated September 28, 2000, and recorded among the Land Records of
Montgomery County, Maryland in Liber 18441, folio 126 (the " Original Deed of
                                                             ----------------
Trust") on certain improved real property located in Gaithersburg, Maryland.
-----

     C. Payee has purchased the Original Note from its holder.

     D. Maker has requested and Payee has agreed to make certain amendments to
the Original Note, including changing the interest rate and the terms of
payment, and increasing the original principal amount from ELEVEN MILLION THREE
HUNDRED NINETY THOUSAND AND NO/100 DOLLARS ($11,390,000.00) to FIFTEEN MILLION
FIVE HUNDRED THOUSAND AND NO/100 DOLLARS ($15,500,000.00). The Original Note is
being amended and restated in its entirety to reflect such amendments.

     E. The Original Deed of Trust is concurrently being amended and restated
pursuant to the terms of the Security Instrument (hereinafter defined).

     NOW, THEREFORE, in consideration of the premises and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Maker and Payee agree that the Original Note is hereby amended
and restated in its entirety as follows (as amended and restated, the "NOTE"):

     For value received, Maker, with an address at 9600 Blackwell Road, Suite
200, Rockville, Maryland 20850, jointly and severally, promises to pay to the
order of Payee, at its principal place of business at 1285 Avenue of the
Americas, 11th Floor, New York, New York 10019, or at such place as the holder
hereof may from time to time designate

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in writing, the principal sum of FIFTEEN MILLION FIVE HUNDRED THOUSAND AND
NO/100 DOLLARS ($15,500,000.00), in lawful money of the United States of
America, with interest thereon to be computed on the unpaid principal balance
from time to time outstanding at the Interest Rate (as hereinafter defined), and
to be paid in installments as follows:

     A.   A payment of interest only on the date the Loan (as hereinafter
          defined) is funded to Maker, representing interest to be accrued from
          the date of such funding through and including May 10, 2004;

     B.   An interest-only payment (such payment, the " Interest Only Monthly
                                                        ---------------------
          Payment Amount") calculated in accordance with the terms of this Note
          --------------
          on the eleventh day of June, 2004 and on the eleventh day of each
          calendar month thereafter (each, a " Payment Date") up to and
                                               ------------
          including the eleventh day of May, 2009;

     C.   A constant payment of $93.529.09 (such amount, the "Monthly P&I
                                                              -----------
          Payment Amount"; the Interest Only Monthly Payment Amount and the
          --------------
          Monthly P&I Payment Amount are hereinafter, the " Monthly Debt Service
                                                            --------------------
          Payment Amount" on the eleventh day of June, 2009 and on each Payment
          --------------
          Date thereafter up to and including the eleventh day of April, 2014;
          each of such payments to be applied (a) to the payment of interest
          computed at the Interest Rate; and (b) the balance applied toward the
          reduction of the principal sum;

and the balance of said principal sum together with all accrued and unpaid
interest thereon shall be due and payable on the eleventh day of May, 2014 (the
"Maturity Date"). Payee shall have the right from time to time, in its sole
 -------------
discretion, upon not less than thirty (30) days prior written notice to Maker,
to change the Payment Date to a different calendar day each month which is not
more than five (5) days earlier nor more than five (5) days later than the
eleventh day of each calendar month. Interest on the principal sum of this Note
shall be calculated on the basis of the actual number of days elapsed in the
related interest accrual period over a three hundred sixty (360) day year. The
first interest accrual period hereunder shall commence on and include the date
that principal is advanced hereunder and shall end on and include the next tenth
(10th) day of a calendar month; unless principal is advanced on the tenth (10th)
day of a month, in which case the first interest accrual period shall consist of
only such tenth (10th) day. Each interest accrual period thereafter shall
commence on the eleventh (11th) day of each calendar month during the term of
this Note and shall end on and include the tenth (10th) day of the next
occurring calendar month; provided, however, that if Payee shall have elected to
change the Payment Date as aforesaid, Payee shall have the option, but not the
obligation, to adjust the interest accrual period correspondingly. All amounts
due under this Note shall be payable without setoff, counterclaim or any other
deduction whatsoever.

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     1. The term "Interest Rate" as used in this Note shall mean a rate of Six
                  -------------
and 06/100 percent (6.06%) per annum.

     2. This Note is evidence of that certain loan made by Payee to Maker
contemporaneously herewith (the "Loan"). This Note is secured by (a) an Amended
                                 ----
and Restated Deed of Trust, Assignment of Leases and Rents and Security
Agreement of even date herewith given by Maker for the use and benefit of Payee
covering the estate of Maker in certain premises as more particularly described
therein (the "Security Instrument"), (b) an Assignment of Leases and Rents of
              -------------------
even date herewith executed by Maker in favor of Payee (the "Assignment of
                                                             -------------
Leases"), (c) a Cash Management Agreement of even date herewith by and between
------
Maker and Payee (the "Cash Management Agreement") and (d) the other Loan
                      -------------------------
Documents (as hereinafter defined). The term "Loan Documents" as used in this
                                              --------------
Note relates collectively to this Note, the Security Instrument, the Assignment
of Leases, the Cash Management Agreement and any and all other documents
securing, evidencing, or guaranteeing all or any portion of the Loan or
otherwise executed and/or delivered in connection with this Note and the Loan.

     3. If any sum payable under this Note is not paid on the date on which it
is due, Maker shall pay to Payee upon demand an amount equal to the lesser of
five percent (5%) of such unpaid sum or the maximum amount permitted by
applicable law in order to defray a portion of the expenses incurred by Payee in
handling and processing such delinquent payment and to compensate Payee for the
loss of the use of such delinquent payment. If the day when any payment required
under this Note is due is not a Business Day (as hereinafter defined), then
payment shall be due on the first Business Day thereafter. The term "Business
                                                                     --------
Day" shall mean a day other than (i) a Saturday or Sunday, or (ii) any day on
---
which banking and savings and loan institutions in New York are authorized or
obligated by law or executive order to be closed.

     4. The whole of the principal sum of this Note, together with all interest
accrued and unpaid thereon and all other sums due under the Loan Documents (all
such sums hereinafter collectively referred to as the "Debt"), shall without
                                                       ----
notice become immediately due and payable at the option of Payee if any payment
required in this Note is not paid on the date on which it is due or upon the
happening of any other Event of Default (as defined in the Security Instrument).
In the event that it should become necessary to employ counsel to collect or
enforce the Debt or to protect or foreclose the security therefor, Maker also
shall pay on demand all costs of collection incurred by Payee, including
attorneys' fees and costs reasonably incurred for the services of counsel
whether or not suit be brought.

     5. Maker does hereby agree that upon the occurrence of an Event of Default
(including upon the failure of Maker to pay the Debt in full on the Maturity
Date), Payee shall be entitled to receive and Maker shall pay interest on the
entire unpaid principal sum and any other amounts due at a rate (the "Default
                                                                      -------
Rate") equal to the lesser of (a) the maximum rate permitted by applicable law,
----
or (b) five percent (5%) above the Interest Rate. The Default Rate shall be
computed from the occurrence of the Event of Default until the date Maker cures
the Event of Default and such cure is accepted by Payee. This charge shall be
added to the Debt and shall be secured by the Security Instrument. This

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paragraph, however, shall not be construed as an agreement or privilege to
extend the date of the payment of the Debt, nor as a waiver of any other right
or remedy accruing to Payee by reason of the occurrence of any Event of Default.

     6. This Note may not be prepaid prior to the Maturity Date; provided,
however, Maker shall have the right and option to release the Trust Property (as
defined in the Security Instrument) from the lien of the Security Instrument in
accordance with the terms and provisions set forth in Paragraph 47 of the
Security Instrument (the "Defeasance Option"). Notwithstanding the foregoing
                          -----------------
sentence, Maker shall have the privilege to prepay the entire principal balance
of this Note and any other amounts outstanding on any scheduled payment date on
or after the date that is three (3) months immediately preceding the Maturity
Date (hereinafter, the "Optional Prepayment Date") upon thirty (30) days' prior
                        ------------------------
written notice to Payee, without payment of the Yield Maintenance Premium (as
defined in the Security Instrument) or any other premium or penalty so long as
no Event of Default has occurred and is continuing. If prior to the Optional
Prepayment Date and following the occurrence of any Event of Default, Maker
shall tender payment of an amount sufficient to satisfy the Debt at any time
prior to a sale of the Trust Property, either through foreclosure or the
exercise of the other remedies available to Payee under the Security Instrument,
such tender by Maker shall be deemed to be voluntary and Maker shall pay, in
addition to the Debt, the Yield Maintenance Premium, if any, that would be
required under the Defeasance Option.

     7. (a) From and after the date hereof, Maker shall cause all Rents (as
defined in the Security Instrument) to be deposited in the Clearing Account (as
defined in the Cash Management Agreement) directly by Tenants at the Trust
Property. Provided that a Sweep Period (as defined in the Cash Management
Agreement) does not exist, Maker shall have the right to cause all available
funds in the Clearing Account to be transferred to an account of the Maker of
the Maker's election. Commencing on the first day of each Collection Period (as
defined in the Cash Management Agreement) during any Sweep Period (as defined in
the Cash Management Agreement), all Rents deposited in the Clearing Account
shall be transferred in accordance with the terms and conditions of the Cash
Management Agreement to the Cash Collateral Account (as defined in the Cash
Management Agreement) and shall be allocated in the following order of priority:

               (i)  First, to fund the Tax and Insurance Escrow Fund Account (as
                    established pursuant to the Cash Management Agreement) until
                    the amount on deposit therein is equal to the amount
                    required to be deposited in the Tax and Insurance Escrow
                    Fund on the related Payment Date in accordance with the
                    terms and conditions of the Security Instrument;

               (ii) Next, to fund the Monthly Debt Service Subaccount (as
                    established pursuant to the Cash Management Agreement) until
                    the amount on deposit therein is equal to the Monthly Debt
                    Service Payment Amount;

<PAGE>

               (iii) Next, to fund the Monthly Debt Service Subaccount with any
                    other amounts due to the Payee under the Loan Documents not
                    otherwise addressed by this paragraph;

               (iv) Next, to fund the Replacement Escrow Fund Subaccount (as
                    established pursuant to the Cash Management Agreement) until
                    the amount on deposit therein is equal to the amount
                    required to be deposited in the Replacement Escrow Fund (as
                    defined in the Security Instrument) on the related Payment
                    Date in accordance with the terms and conditions of the
                    Security Instrument;

               (v)  Next, to fund the Rollover Escrow Fund Subaccount (as
                    established pursuant to the Cash Management Agreement) until
                    the amount on deposit therein is equal to the amount
                    required to be deposited in the Rollover Escrow Fund (as
                    defined in the Security Instrument) on the related Payment
                    Date in accordance with the terms and conditions of the
                    Security Instrument; and

               (vi) Lastly, and subject to the terms and conditions of the Cash
                    Management Agreement, to fund the Borrower Remainder
                    Subaccount (as established pursuant to the Cash Management
                    Agreement) any Rents remaining after funding the foregoing
                    allocations.

          (b) Nothing in this paragraph 7 shall limit, reduce or otherwise
affect Maker's obligations to make payments of the Monthly Debt Service Payment
Amount, payments to the Tax and Insurance Escrow Fund, the Replacement Escrow
Fund and Rollover Escrow Fund due hereunder and under the other Loan Documents,
whether or not Rents are available to make such payments.

     8. It is expressly stipulated and agreed to be the intent of Maker and
Payee at all times to comply with applicable state law or applicable United
States federal law (to the extent that it permits Payee to contract for, charge,
take, reserve, or receive a greater amount of interest than under state law) and
that this paragraph shall control every other covenant and agreement in this
Note and the other Loan Documents. If the applicable law (state or federal) is
ever judicially interpreted so as to render usurious any amount called for under
this Note or under any of the other Loan Documents, or contracted for, charged,
taken, reserved, or received with respect to the Debt, or if Payee's exercise of
the option to accelerate the Maturity Date, or if any prepayment or the exercise
of any Defeasance Option by Maker results in Maker having paid any interest in
excess of that permitted by applicable law, then it is Payee's express intent
that all excess amounts theretofore collected by Payee shall be credited on the
principal balance of this Note and all other Debt and the provisions of this
Note and the other Loan Documents immediately be deemed reformed and the amounts
thereafter collectible hereunder and thereunder

<PAGE>

reduced, without the necessity of the execution of any new documents, so as to
comply with the applicable law, but so as to permit the recovery of the fullest
amount otherwise called for hereunder or thereunder. All sums paid or agreed to
be paid to Payee for the use, forbearance, or detention of the Debt shall, to
the extent permitted by applicable law, be amortized, prorated, allocated, and
spread throughout the full stated term of the Debt until payment in full so that
the rate or amount of interest on account of the Debt does not exceed the
maximum lawful rate from time to time in effect and applicable to the Debt for
so long as the Debt is outstanding. Notwithstanding anything to the contrary
contained herein or in any of the other Loan Documents, it is not the intention
of Payee to accelerate the maturity of any interest that has not accrued at the
time of such acceleration or to collect unearned interest at the time of such
acceleration.

     9. This Note may not be modified, amended, waived, extended, changed,
discharged or terminated orally or by any act or failure to act on the part of
Maker or Payee, but only by an agreement in writing signed by the party against
whom enforcement of any modification, amendment, waiver, extension, change,
discharge or termination is sought. Whenever used, the singular number shall
include the plural, the plural the singular, and the words 'Payee" and "Maker"
                                                            -----       -----
shall include their respective successors, assigns, heirs, executors and
administrators. If Maker consists of more than one person or party, the
obligations and liabilities of each such person or party shall be joint and
several.

     10. Maker and all others who may become liable for the payment of all or
any part of the Debt do hereby severally waive presentment and demand for
payment, notice of dishonor, protest, notice of protest, notice of nonpayment,
notice of intent to accelerate the maturity hereof and of acceleration. No
release of any security for the Debt or any person liable for payment of the
Debt, no extension of time for payment of this Note or any installment hereof,
and no alteration, amendment or waiver of any provision of the Loan Documents
made by agreement between Payee and any other person or party shall release,
modify, amend, waive, extend, change, discharge, terminate or affect the
liability of Maker, and any other person or party who may become liable under
the Loan Documents for the payment of all or any part of the Debt.

     11. (a) Subject to the qualifications below, Payee shall not enforce the
liability and obligation of Maker to perform and observe the obligations
contained in this Note, the Security Instrument or the other Loan Documents by
any action or proceeding wherein a money judgment shall be sought against Maker,
except that Payee may bring a foreclosure action, an action for specific
performance or any other appropriate action or proceeding to enable Payee to
enforce and realize upon its interest under this Note, the Security Instrument
and the other Loan Documents, or in the Trust Property, the Rents, or any other
collateral given to Payee pursuant to the Loan Documents; provided, however,
                                                          --------  -------
that, except as specifically provided herein, any judgment in any such action or
proceeding shall be enforceable against Maker only to the extent of Maker's
interest in the Trust Property, in the Rents and in any other collateral given
to Payee, and Payee, by accepting this Note, the Security Instrument and the
other Loan Documents, agrees that it shall not sue for, seek or demand any
deficiency judgment against Maker in any such action or proceeding under or by
reason of or under or in connection with this Note, the

<PAGE>

Security Instrument or the other Loan Documents. The provisions of this
paragraph shall not, however, (1) constitute a waiver, release or impairment of
any obligation evidenced or secured by any of the Loan Documents; (2) impair the
right of Payee to name Maker as a party defendant in any action or suit for
foreclosure and sale under the Security Instrument; (3) affect the validity or
enforceability of or any guaranty made in connection with the Loan or any of the
rights and remedies of the Payee thereunder; (4) impair the right of Payee to
obtain the appointment of a receiver; or (5) impair the enforcement of the
Assignment of Leases. Notwithstanding anything to the contrary contained in this
Note or in any of the other Loan Documents, Maker shall be fully and personally
liable and subject to legal action to the extent of any loss, damage (including
damage resulting from the diminution in value of the Trust Property as the
result of subsection (iv) below), cost, expense, liability, claim or other
obligation incurred by Payee (including attorneys' fees and costs reasonably
incurred) arising out of or in connection with the following:

               (i)  fraud or intentional misrepresentation or failure to
                    disclose a material fact by Maker, any of Maker's officers,
                    agents, attorneys, principals, general partners, managing
                    members or employees, or any guarantor or indemnitor in
                    connection with the Loan, including without limitation, the
                    origination of the Loan and the performance of Maker's
                    obligations under the Loan Documents;

               (ii) the gross negligence or willful misconduct of Maker;

               (iii) physical waste of the Trust Property;

               (iv) the breach of any representation, warranty, covenant or
                    indemnification provision in the Loan Documents concerning
                    environmental law, hazardous substances or asbestos;

               (v)  the removal or disposal of any portion of the Trust Property
                    during the continuance of an Event of Default;

               (vi) the misapplication or conversion by Maker of (A) any
                    insurance proceeds paid by reason of any loss, damage or
                    destruction to the Trust Property, (B) any awards or other
                    amounts received in connection with the condemnation of all
                    or a portion of the Trust Property, (C) any Rents following
                    an Event of Default, or during a Sweep Period, or (D) any
                    Rents paid more than one month in advance;

               (vii) the failure to pay charges for labor or materials or taxes
                    or other charges that can create liens on any portion of the
                    Trust Property;

<PAGE>

               (viii) all tenant security deposits or other refundable deposits
                    paid to or held by Maker or any other person or entity in
                    connection with the Leases (as defined in the Security
                    Instrument) which are not applied in accordance with the
                    terms of the applicable Leases;

               (ix) the failure to obtain and maintain the fully paid for
                    Policies (as defined in the Security Instrument) in
                    accordance with Paragraph 2 of the Security Instrument;
                                    -----------

               (x)  the failure of Maker or, if Manager is an affiliate of
                    Maker, Manager to strictly comply with the terms of the Cash
                    Management Agreement;

               (xi) the failure of Maker to strictly comply with the terms and
                    provisions of Section 10 (mm) of the Security Instrument;
                    and

               (xii) any Tenant in Common commences an action for partition.

          (b) In addition, Maker shall be fully and personally liable for,
hereby unconditionally guarantees payment to Payee of, and hereby agrees to pay,
(i) all Rent which may now or hereafter be due under the Heller Ehrman Lease for
the Additional Premises (as such term is defined in Section 49.1 of the Heller
Ehrman Lease) in accordance with Section 49 of the Heller Ehrman Lease if Heller
Ehrman fails to pay Rent for the Additional Premises in accordance with Section
49 of the Heller Ehrman Lease, and (ii) all Rent which may now or hereafter be
due under the Heller Ehrman Lease in respect of its entire leased premises if,
in connection with a claim by Heller Ehrman that Borrower has failed to comply
with Section 48 of the Heller Ehrman Lease, Heller Ehrman fails or refuses to
pay Rent due under the Heller Ehrman Lease. The recourse liability and
obligations of Maker under Paragraph 11(b)(i) are collectively referred to as
the "Springing Heller Ehrman Additional Premises Rent Guaranty" and the recourse
     ---------------------------------------------------------
liability and obligations of Maker under Paragraph 11(b)(ii) are collectively
referred to as the "Springing Heller Ehrman Leased Premises Rent Guaranty". So
                    -----------------------------------------------------
long as no Event of Default shall have occurred and remain uncured, Maker may
make a written request that Payee make a determination whether the Springing
Heller Ehrman Additional Premises Rent Guaranty or the Springing Heller Ehrman
Leased Premises Rent Guaranty (as the case may be) shall continue to be
required. Payee shall make its determination as hereinafter set forth in this
Paragraph 11(b).

          Payee's determination of any release of the Springing Heller Ehrman
     Additional Premises Rent Guaranty and the Springing Heller Ehrman Leased
     Premises Rent Guaranty shall be subject to satisfaction of each of the
     following conditions precedent:

          (1)  Maker, at its sole cost and expense, shall have promptly provided
               to Payee all documentation and information

<PAGE>

               determined by Payee in Payee's reasonable discretion to be
               necessary for Payee to make the determination as set forth in
               this Paragraph 11(b), including, without limitation, copies of
               the Office Leases (as hereinafter defined) related to the
               Additional Premises and the Heller Ehrman Space (as the case may
               be), rent rolls, tenant estoppel certificates, and property
               operating and financial statements, and any other evidence of
               performance, operation or condition of the Trust Property related
               to the Additional Premises and the Heller Ehrman Space (as the
               case may be) requested by Payee in its reasonable discretion;

          (2)  The Additional Premises in respect of Maker's request for a
               release from the Springing Heller Ehrman Additional Premises Rent
               Guaranty, and the Heller Ehrman Space in respect of Maker's
               request for a release from the Springing Heller Ehrman Leased
               Premises Rent Guaranty, if Heller Ehrman is not the party paying
               Rent on the Additional Premises or the Heller Ehrman Space, as
               applicable, is occupied in its entirety by one or more
               unaffiliated, arms-length office tenants with credit determined
               by Payee to be equal to or better than the credit of Heller
               Ehrman as of the date hereof (the "Office Tenants") pursuant to
                                                  --------------
               bona fide written lease agreements which comply with the terms
               and conditions of the Security Instrument and were approved (or
               deemed approved) by Payee (the "Office Leases"); all Office
                                               -------------
               Tenants under all Office Leases shall have been in actual
               occupancy of, conducting business from, and paying full unabated
               rent and additional rent for, their respective leased premises;
               no Office Tenants under any Office Leases are insolvent or the
               subject of any proceeding or action relating to a bankruptcy,
               reorganization or other arrangement pursuant to federal
               bankruptcy law; Maker shall have performed all of its obligations
               of an inducement nature under each Office Lease with an Office
               Tenant (including payment and performance of all tenant
               improvement work); and all Office Leases with Office Tenants are
               in full force and effect and neither landlord nor tenant
               thereunder is in default;

          (3)  All Office Leases with Office Tenants provide for an initial term
               which is at least five (5) years;

          (4)  The aggregate Rent paid by the Office Tenants under the Office
               Leases shall be equal to or greater than the Rent which Heller
               Ehrman is required to pay under the Heller Ehrman Lease for the
               Additional Premises in respect of Maker's request for a release
               from the Springing Heller

<PAGE>

               Ehrman Additional Premises Rent Guaranty and the aggregate Rent
               paid by the Office Tenants under the Office Leases shall be equal
               to or greater than the Rent which Heller Ehrman is required to
               pay under the Heller Ehrman Lease for the Heller Ehrman Space in
               respect of Maker's request for a release from the Springing
               Heller Ehrman Leased Premises Rent Guaranty;

          (5)  Maker shall have caused all Office Tenants under Office Leases to
               deliver to Payee current estoppel certificates in form and
               substance acceptable to Payee confirming, among other things,
               that (1) each Office Lease is in full force and effect, (2) all
               Office Tenants have paid full, unabated base rent and additional
               rent through the end of the calendar month in which the estoppel
               certificate is delivered to Payee, (3) all Office Tenants are in
               occupancy of and conducting business from their respective leased
               premises and (4) all obligations of the Maker, as landlord, of an
               inducement nature have been satisfied or irrevocably waived by
               the Office Tenant; and

          (6)  Maker shall have paid all reasonable and actual out-of-pocket
               costs and expenses of Payee in connection with Payee's
               determination under this Paragraph 11(b), and the documentation
               and release of the Springing Heller Ehrman Additional Premises
               Rent Guaranty or Springing Heller Ehrman Leased Premises Rent
               Guaranty (as the case may be), including without limitation, all
               reasonable attorneys' fees, costs and expenses.

     (c) Notwithstanding anything to the contrary in this Note or any of the
Loan Documents, (1) Payee shall not be deemed to have waived any right which
Payee may have under Section 506(a), 506(b), 1111(b) or any other provisions of
the U.S. Bankruptcy Code to file a claim for the full amount of the Debt secured
by the Security Instrument or to require that all collateral shall continue to
secure all of the Debt owing to Payee in accordance with the Loan Documents, and
(2) the Debt shall be fully recourse to Maker in the event that: (i) the first
full monthly payment of principal and interest under this Note is not paid when
due; (ii) Maker fails to maintain its status as a single purpose entity, as
required by, and in accordance with the terms and provisions of, the Security
Instrument (except with respect to the terms and provisions of clause (j) of
Paragraph 11 thereof); (iii) Maker fails to obtain Payee's prior written consent
to any subordinate financing or other voluntary lien encumbering the Trust
Property; (iv) Maker fails to obtain Payee's prior written consent to any
assignment, transfer, or conveyance of the Trust Property or any interest
therein as required by the Security Instrument, (v) a receiver, liquidator or
trustee of Maker or of any guarantor shall be appointed or if Maker or any
guarantor shall be adjudicated a bankrupt or insolvent, or if any petition for
bankruptcy, reorganization or

<PAGE>

arrangement pursuant to federal bankruptcy law, or any similar federal or state
law, shall be filed by, consented to, or acquiesced in by, Maker or any
guarantor or if any proceeding for the dissolution or liquidation of Maker or of
any guarantor shall be instituted by Maker or any guarantor, or (vi) Maker or
any guarantor (or any person comprising such guarantor) or any Related Party of
any of the foregoing shall, in connection with any enforcement action or
exercise or assertion of any right or remedy by or on behalf of Payee under or
in connection with this Note, the Security Instrument or any of the other Loan
Documents, asserts a defense, seeks judicial intervention or injunctive or other
equitable relief of any kind or asserts in a pleading filed in connection with a
judicial proceeding any defense against Payee or any right in connection with
any security for the Loan which the court in such action or proceeding
determines is not made in good faith and is without merit (in respect of a
defense) or unwarranted (in respect of a request for judicial intervention or
injunctive or other equitable relief). "Related Party" shall mean any person or
entity which owns a direct or indirect interest in Maker or any guarantor (or
any person comprising such guarantor), or which is owned or controlled by or
under common ownership or control with Maker or any such guarantor.

     12. Maker (and the undersigned representative of Maker, if any) represents
that Maker has full power, authority and legal right to execute, deliver and
perform its obligations pursuant to this Note, the Security Instrument and the
other Loan Documents and that this Note, the Security Instrument and the other
Loan Documents constitute valid and binding obligations of Maker.

     13. All notices or other communications required or permitted to be given
pursuant hereto shall be given in the manner specified in the Security
Instrument directed to the parties at their respective addresses as provided
therein.

     14. MAKER HEREBY AGREES NOT TO ELECT A TRIAL BY JURY OF ANY ISSUE TRIABLE
OF RIGHT BY JURY, AND WAIVES ANY RIGHT TO TRIAL BY JURY FULLY TO THE EXTENT THAT
ANY SUCH RIGHT SHALL NOW OR HEREAFTER EXIST WITH REGARD TO THE LOAN DOCUMENTS,
OR ANY CLAIM, COUNTERCLAIM OR OTHER ACTION ARISING IN CONNECTION THEREWITH. THIS
WAIVER OF RIGHT TO TRIAL BY JURY IS GIVEN KNOWINGLY AND VOLUNTARILY BY MAKER,
AND IS INTENDED TO ENCOMPASS INDIVIDUALLY EACH INSTANCE AND EACH ISSUE AS TO
WHICH THE RIGHT TO A TRIAL BY JURY WOULD OTHERWISE ACCRUE. PAYEE IS HEREBY
AUTHORIZED TO FILE A COPY OF THIS PARAGRAPH IN ANY PROCEEDING AS CONCLUSIVE
EVIDENCE OF THIS WAIVER BY MAKER.

     15. This Note shall be governed by and construed in accordance with the
laws of the State in which the Trust Property is located and the applicable laws
of the United States of America.

     16. Any capitalized term used in this Note and not defined herein shall
have the meaning given to such term in the Security Instrument.

<PAGE>

     17. This Note may be executed in one or more counterparts, each of which
shall be deemed to constitute an original, but all of which, when taken
together, shall constitute one and the same instrument.

     18. This Note does not extinguish the outstanding indebtedness evidenced by
the Original Note or discharge or release the Original Deed of Trust or any
other security, and the parties do not intend this Note to be a substitution or
novation of the original indebtedness or instruments securing same.

                            [SIGNATURE PAGE FOLLOWS]

<PAGE>

Maker has duly executed this Note the day and year first above written.

                                        MAKER:

                                        ARGO ORCHARD RIDGE, LC, a
                                        Maryland limited liability company

                                        By: ARGO ORCHARD RIDGE MANAGER, INC., a
                                            Maryland corporation, its Managing
                                            Member

                                        By: /s/ Richard L. Perlmutter
                                            ------------------------------------
                                        Name: Richard L. Perlmutter
                                        Title: President

<PAGE>

                                        FOULGER LAND LIMITED PARTNERSHIP, a
                                        Virginia limited partnership

                                        By: SID FOULGER (ORCHARD RIDGE), INC., a
                                            Maryland corporation, its General
                                            Partner

                                        By: /s/ Clayton F. Foulger
                                            ------------------------------------
                                        Name: Clayton F. Foulger
                                        Title: Vice President

<PAGE>

     UBS REAL ESTATE INVESTMENTS INC., a Delaware corporation, holder of the
Original Note, signs below to acknowledge its consent to the terms of this Note.

                                        PAYEE:

                                        UBS REAL ESTATE INVESTMENTS INC., a
                                        Delaware corporation

                                        By: /s/ Peter A. Smith
                                            ------------------------------------
                                        Name: Peter A. Smith
                                        Title: Managing Director

                                        By: /s/ Matthew L. Kirsch
                                            ------------------------------------
                                        Name: Matthew L. Kirsch
                                        Title: Director<PAGE>

                                                                    EXHIBIT 10.6

Upon recordation, return to:
Marvin W. Ehrlich, Esq.
Greenberg Traurig, LLP
1750 Tysons Boulevard
Suite 1200
McLean, VA 22102

        Wells Fargo Bank, N.A., as trustee for the registered holders of
          LB-UBS Commercial Mortgage Trust 2004-C4, Commercial Mortgage
                    Pass-Through Certificates, Series 2004-C4

                                   ----------

                                 LOAN ASSUMPTION

                                       AND

                             SUBSTITUTION AGREEMENT

                                   ----------

                          Date: As of September 8, 2006

                                   ----------

<PAGE>

                   LOAN ASSUMPTION AND SUBSTITUTION AGREEMENT
                   ------------------------------------------

     THIS LOAN ASSUMPTION AND SUBSTITUTION AGREEMENT (this "AGREEMENT") is made
and entered into as of September 8, 2006, by and among ARGO Orchard Ridge, LC, a
Maryland limited liability company ("ARGO") and FOULGER LAND ORCHARD RIDGE 2006,
LLC, a Maryland limited liability company ("FOULGER LAND"), as
tenants-in-common, having an address of c/o Columbia Equity Trust, Inc., 1750 H
Street, NW, Suite 500, Washington, DC 20006, Attention: Oliver T. Carr, III
("ASSUMING BORROWER"), Columbia Equity, LP, a Virginia limited partnership
having an address at 1750 H Street, NW, Suite 500, Washington, DC 20006,
Attention: Oliver T. Carr, III (individually and collectively, if more than one,
"ASSUMING INDEMNITOR"), ARGO Orchard Ridge, LC, a Maryland limited liability
company and Foulger Land Limited Partnership, a Virginia limited partnership
("FOULGER"), as tenants-in-common, having an address at 9600 Blackwell Road,
Suite 200, Rockville, MD 20850 (collectively, the "ORIGINAL BORROWER"), and
Clayton Foulger, an individual resident of the State of Maryland, having an
address at 11101 Piney Meeting House Road, Potomac, MD 20854 and Bryant Foulger,
an individual resident of the State of Maryland, having an address at 11105
Piney Meeting House Road, Potomac, MD 20854, John Austin, an individual resident
of the Commonwealth of Virginia whose address is 2836 Linden Lane, Falls Church,
Virginia 22042, Richard Perlmutter, an individual resident of the State of
Maryland, having an address at 11113 Crippelgate Road, Potomac, MD 20854, and
Brent Pratt, an individual resident of the State of Maryland, having an address
at 11113 Piney Meeting House Road, Potomac, MD 20854 (individually and
collectively, if more than one, "ORIGINAL INDEMNITOR") in favor of Wells Fargo
Bank, N.A., as trustee for the registered holders of LB-UBS Commercial Mortgage
Trust 2004-C4, Commercial Mortgage Pass-Through Certificates, Series 2004-C4,
whose mailing address is c/o Wachovia Securities, Commercial Real Estate
Services, 8739 Research Drive-URP4, Charlotte, NC 28288-1075 (28262-1075 for
overnight deliveries), Attn: Portfolio Manager ("LENDER").

                                    RECITALS
                                    --------

     A. All First Bank ("ALL FIRST"), made a loan to Original Borrower in the
original principal amount of $11,390,000.00 (the "LOAN"), which was increased to
$15,500,000.00, amended and restated on May 7, 2004 pursuant to the Loan
Documents (as hereinafter defined) in favor of UBS Real Estate Investments,
Inc., (the "ORIGINAL LENDER"). The Loan is evidenced and secured by the
following documents executed in favor of Original Lender by Original Borrower
and Original Indemnitor:

     (1)  Amended and Restated Deed of Trust Note dated May 7, 2004, payable by
          Original Borrower to Original Lender in the principal amount of
          $15,500,000.00 (the "NOTE");

     (2)  Amended and Restated Deed of Trust, Assignment of Leases and Rents and
          Security Agreement, dated May 7, 2004 granted by Original Borrower to
          Sarah Eckert Webb and Terrence M. Sullivan, as Trustee for the benefit
          of Original Lender recorded in Book 27286, Page 095, in the real
          estate records of

<PAGE>

          Montgomery County, MD ("RECORDER'S OFFICE") (the "MORTGAGE");

     (3)  Assignment of Leases and Rents of even date with the Note granted by
          Original Borrower to Original Lender, recorded in Book 27286, Page 170
          in the Recorder's Office (the "ASSIGNMENT");

     (4)  UCC-1 financing statements with Original Borrower as debtor and
          Original Lender as secured party, filed with the Recorder's Office on
          May 10, 2004 in Liber 27286, Folio 200, assigned March 31, 2005 in
          Liber 29573, Folio 69 and filed with the Department of Assessments and
          Taxation of the State of Maryland. on May 12, 2004 as Lien Number
          181191059 and the Virginia State Corporation Commission on May 12,
          2004 as File Number 04-05-12-7322-2;

     (5)  Indemnity and Guaranty Agreement by and between Original Indemnitor
          and Original Lender of even date with the Note (the "INDEMNITY
          AGREEMENT");

     (6)  Hazardous Substances Indemnity Agreement by and among Original
          Borrower, Original Indemnitor and Original Lender of even date with
          the Note (the "ENVIRONMENTAL INDEMNITY AGREEMENT');

     (7)  Assignment of Warranties and Other Contract Rights from Original
          Borrower to Original Lender of even date with the Note; and

     (8)  Cash Management Agreement by and among Original Borrower, Original
          Lender and FP-Argo Management II, LC of even date with the Note.

     (9)  First Amendment to Cash Management Agreement by and among Assuming
          Borrower, Lender and Columbia Equity Services, LLC of even date
          herewith.

The foregoing documents, together with any and all other documents executed by
Original Borrower and/or Original Indemnitor in connection with the Loan, are
collectively called the "LOAN DOCUMENTS." As used herein, the term "ASSUMING
OBLIGORS" shall mean Assuming Borrower and Assuming Indemnitor; and the term
"ORIGINAL OBLIGORS" shall mean Original Borrower and Original Indemnitor.

     B. Original Lender assigned, sold and transferred its interest in the Loan
and all Loan Documents to Lender and Lender is the current holder of all of
Original Lender's interest in the Loan and Loan Documents.

     C. Original Borrower continues to be the owner of the Property (as defined
below).

     D. Pursuant to that certain Agreement of Purchase and Sale dated April 25,
2006 (as amended and as assigned to Assuming Borrower, the "SALES AGREEMENT"),
Sellers (as defined in the Sales Agreement) agreed to sell, and Assuming
Borrower agreed to purchase, Seller's ownership interests in entities that own
that certain real property more particularly described on EXHIBIT A attached
                                                          ---------
hereto, together with all other property encumbered by the Mortgage and the
other Loan Documents (collectively, the "PROPERTY"). The Sales Agreement
requires that the

                                       -2-

<PAGE>

Assuming Borrower assume the Loan and the obligations of Original Borrower under
the Loan Documents, and conditions the closing of the transactions contemplated
by the Sales Agreement, which include the transfer of the Beneficial ownership
of the Original Borrower to the Assuming Borrower (collectively, the
"TRANSACTIONS") upon the Lender's consent to the Transactions and the assumption
of the Loan.

     E. Pursuant to Section 13 of the Mortgage, any sale or transfer of the
Property and certain direct and indirect interests therein requires the Lender's
prior written consent. Original Borrower and Assuming Borrower have requested
that Lender consent to the Transactions, subject to the Mortgage and the other
Loan Documents, and to the assumption by Assuming Borrower of the Loan and the
assumption by Assuming Obligors of the obligations of Original Obligors under
the Loan Documents, to the extent set forth herein (the "ASSUMPTION").

     F. Lender is willing to consent to the Transactions, subject to the
Mortgage and the other Loan Documents, and to the Assumption on and subject to
the terms and conditions set forth in this Agreement and in the Mortgage and in
the other Loan Documents.

     G. Lender, Original Obligors and Assuming Obligors by their respective
executions hereof, evidence their consent to the Transactions and the Assumption
as hereinafter set forth.

                             STATEMENT OF AGREEMENT
                             ----------------------

     In consideration of the mutual covenants and agreements set forth herein,
the parties hereto hereby agree as follows:

     1. REPRESENTATIONS, WARRANTIES, AND COVENANTS OF ORIGINAL OBLIGORS, RELEASE
        ------------------------------------------------------------------------
OF LENDER.
----------

          (a) Original Obligors hereby represent to Lender, as of the date
hereof, that (i) simultaneously with the execution and delivery hereof, Original
Borrower has conveyed and transferred beneficial ownership of the Property to
Assuming Borrower; (ii) simultaneously with the execution and delivery hereof,
Original Borrower has assigned and transferred to Assuming Borrower title to all
leases, tenancies, security deposits and prorated rents of the Property in
effect as of the date hereof ("LEASES") retaining no rights therein or thereto;
(iii) Original Borrower has not received a mortgage from Assuming Borrower
encumbering the Property to secure the payment of any sums due Original Borrower
or obligations to be performed by Assuming Borrower; (iv) except as may
otherwise be permitted pursuant to the Loan Documents, the Mortgage is a valid
first lien on the Property for the full unpaid principal amount of the Loan and
all other amounts as stated therein; (v) no Event of Default (as defined in the
Mortgage) has occurred and is continuing; (vi) there are no defenses, set-offs
or rights of defense, set-off or counterclaim whether legal, equitable or
otherwise to the obligations evidenced by or set forth in the Loan Documents;
(vii) all provisions of the Loan Documents are in full force and effect, except
as modified herein; (viii) except as may otherwise be permitted pursuant to the
Loan Documents, there are no subordinate liens of any kind covering or relating
to the Property nor are there any mechanics' liens or liens for unpaid taxes or
assessments encumbering the Property, nor has notice of a lien or notice of
intent to file a lien been received; and (ix) the representations and warranties
made by Original Obligors in the Loan Documents

                                      -3-

<PAGE>

or in any other documents or instruments delivered in connection with the Loan
Documents, including, without limitation, all representations and warranties
with respect to environmental matters, are true, on and as of the date hereof,
with the same force and effect as if made on and as of the date hereof.

          (b) Original Obligors hereby covenant and agree that: (i) from and
after the date hereof, Lender may deal solely with Assuming Obligors in all
matters relating to the Loan, the Loan Documents, and the Property; (ii) they
shall not at any time hereafter take (x) a mortgage or other lien encumbering
the Property or (y) a pledge of direct or indirect interests in Assuming
Borrower from Assuming Obligors to secure any sums to be paid or obligations to
be performed by Assuming Obligors so long as any portion of the Loan remains
unpaid; and (iii) Lender has no further duty or obligation of any nature
relating to this Loan or the Loan Documents to Original Obligors. Original
Obligors understand and intend that Lender shall rely on the representations,
warranties and covenants contained herein.

     2. REPRESENTATIONS, WARRANTIES, AND COVENANTS OF ASSUMING OBLIGORS.
        ----------------------------------------------------------------

          (a) Assuming Obligors hereby represent and warrant to Lender, as of
the date hereof, that: (i) simultaneously with the execution and delivery
hereof, Assuming Borrower has purchased from Original Borrower the beneficial
ownership of the Property, and has accepted Original Borrower's assignment of
the Leases; (ii) Assuming Borrower has assumed the performance of Original
Borrower's obligations under the Leases from and after the date hereof; (iii)
Assuming Borrower has not granted to Original Borrower (x) a mortgage or other
lien upon the Property or (y) a pledge of direct or indirect interests in the
Assuming Borrower to secure any debt or obligations owed to Original Borrower;
(iv) to the knowledge of Assuming Obligors, no Default or Event of Default has
occurred or is continuing; (v) to the knowledge of Assuming Obligors, all
provisions of the Loan Documents, as herein modified, are in full force and
effect; (vi) to the knowledge of Assuming Obligors, the representations and
warranties made in the Loan Documents or in any other documents or instruments
delivered in connection with the Loan Documents are true, on and as of the date
hereof; and (vii) Assuming Obligors have reviewed all of the Loan Documents and
consent to the terms thereof.

          (b) Assuming Borrower shall not hereafter, without Lender's prior
consent in accordance with the terms of the Loan Documents, further encumber the
Property or sell or transfer the Property or any interest therein, except as may
be specifically permitted in the Loan Documents. Assuming Obligors have no
knowledge that any of the representations and warranties made by the Original
Obligors herein are untrue, incomplete, or incorrect.

          (c) Assuming Indemnitor hereby represents and warrants to the Lender
that Assuming Indemnitor is an affiliate of the Assuming Borrower and Assuming
Indemnitor will derive substantial economic benefit from the Lender's consent to
the Assumption. The Assuming Indemnitor hereby acknowledges and agrees that the
Assuming Indemnitor has executed this Agreement and agreed to be bound by the
covenants and agreements set forth herein in order to induce the Lender to
consent to the transaction described herein. Accordingly, the Assuming
Indemnitor acknowledges that the Lender would not consent to the transaction
described herein without the execution and delivery by the Assuming Indemnitor
of this Agreement.

                                      -4-

<PAGE>

Assuming Obligors understand and intend that Lender shall rely on the
representations, warranties and covenants contained herein.

     3. ASSUMPTION OF OBLIGATIONS OF BORROWER. Assuming Borrower hereby assumes
        --------------------------------------
the Debt (as defined in the Mortgage) and Assuming Borrower hereby assumes all
the other obligations of Original Borrower of every type and nature set forth in
the Loan Documents in accordance with their respective terms and conditions, as
the same may be modified by this Agreement. Assuming Borrower further agrees to
abide by and be bound by all of the terms of the Loan Documents applicable to
the "Borrower", "Assignor" or "Trustor" (as applicable), in accordance with
their respective terms and conditions, including but not limited to, the
representations, warranties, covenants, assurances and indemnifications therein,
all as though each of the Loan Documents had been made, executed, and delivered
by Assuming Borrower. Assuming Borrower agrees to pay when and as due all sums
due under the Note and agrees to pay, perform, and discharge each and every
other obligation of payment and performance of the "Borrower", "Assignor" or
"Trustor" (as applicable) pursuant to and as set forth in the Loan Documents at
the time, in the manner and otherwise in all respects as therein provided.
Assuming Borrower hereby acknowledges, agrees and warrants that (i) there are no
rights of set-off or counterclaim, nor any defenses of any kind, whether legal,
equitable or otherwise, which would enable Assuming Borrower to avoid or delay
timely performance of its obligations under the Loan Documents, as applicable;
and (ii) there are no monetary encumbrances or liens of any kind or nature
against the Property except those created by the Loan Documents, and all rights,
priorities, titles, liens and equities securing the payment of the Note are
expressly recognized as valid and are in all things renewed, continued and
preserved in force to secure payment of the Note, except as amended herein.

     4. ASSUMPTION OF THE OBLIGATIONS OF THE INDEMNITOR UNDER THE INDEMNITY
        -------------------------------------------------------------------
AGREEMENT AND ENVIRONMENTAL INDEMNITY AGREEMENT; SUBSTITUTION OF INDEMNITOR.
----------------------------------------------------------------------------
From and after the date of this Agreement, the Assuming Indemnitor shall be
obligated and responsible for the performance of each and all of the obligations
and agreements of the "Indemnitor", "Guarantor" and/or "Principal" (collectively
referred to herein as "INDEMNITOR") under the Indemnity Agreement, the
Environmental Indemnity Agreement and the other Loan Documents to which Original
Indemnitor is a party, and the Assuming Indemnitor shall be liable and
responsible for each and all of the liabilities of the Indemnitor thereunder,
and shall be substituted in lieu of and in place of the Original Indemnitor, as
fully and completely as if the Assuming Indemnitor had originally executed and
delivered such Loan Documents as the Indemnitor thereunder, including, without
limitation, all of those obligations, agreements and liabilities which would
have, but for the provisions of this Agreement, been the obligations, agreements
and liabilities of the Original Indemnitor, without regard to when such
obligations, agreements and liabilities arise, accrue or have arisen or accrued,
and without regard to the Indemnitor then responsible or liable therefor at the
time of such accrual. From and after the date hereof, the Assuming Indemnitor
further agrees to abide by and be bound by all of the terms of the Loan
Documents having reference to the Indemnitor, all as though each of the Loan
Documents to which the Original Indemnitor is a party had been made, executed,
and delivered by the Assuming Indemnitor as the Indemnitor. From and after the
date hereof, the Assuming Indemnitor hereby agrees to pay, perform, and
discharge each and every obligation of payment and performance of the Indemnitor
under, pursuant to and as set forth in the Loan Documents at

                                      -5-

<PAGE>

the time, in the manner and otherwise in all respects as therein provided. With
respect to the Environmental Indemnity Agreement, the liability of Assuming
Indemnitor shall be joint and several with that of the Assuming Borrower.

     5. NOTICES TO INDEMNITOR. Without amending, modifying or otherwise
        ----------------------
affecting the provisions of the Loan Documents except as expressly set forth
herein, the Lender shall, from and after the date of this Agreement, deliver any
notices to the Indemnitor which are required to be delivered pursuant to the
Loan Documents, or are otherwise delivered by the Lender thereunder at Lender's
sole discretion, to the Assuming Indemnitor's address set forth above.

     6. CONSENT TO TRANSACTIONS, ASSUMPTION AND SUBSTITUTION OF INDEMNITOR;
        -------------------------------------------------------------------
RELEASE OF ORIGINAL OBLIGORS. Subject to the terms and conditions set forth in
-----------------------------
this Agreement, Lender consents to: (a) the Transactions, subject to the
Mortgage and the other Loan Documents; (b) the assumption by Assuming Borrower
of the Loan and the obligations of Original Borrower under the Loan Documents;
and (c) the assumption by Assuming Indemnitor of the obligations of the Original
Indemnitor under the Loan Documents. Original Obligors are hereby released from
any liability to Lender under any and all of the Loan Documents first arising or
accruing subsequent to the Assumption. Lender's consent to such transfer and
Assumption shall, however, not constitute its consent to any subsequent
transfers of the Property. Original Obligors hereby acknowledge and agree that
the foregoing release shall not be construed to release Original Obligors from
any personal liability under the Note or any of the other Loan Documents for any
act or event occurring or obligation arising prior to or simultaneously with the
closing of the transaction described herein.

     7. RELEASE AND COVENANT NOT TO SUE. Original Obligors and Assuming
        --------------------------------
Obligors, on behalf of themselves and their heirs, successors and assigns,
hereby release and forever discharge Lender, any trustee of the Loan, any
servicer of the Loan, each of their respective predecessors in interest and
successors and assigns, together with the officers, directors, partners,
employees, investors, certificate holders and agents of each of the foregoing
(collectively, the "LENDER PARTIES"), from all debts, accountings, bonds,
warranties, representations, covenants, promises, contracts, controversies,
agreements, claims, damages, judgments, executions, actions, inactions,
liabilities demands or causes of action of any nature, at law or in equity,
known or unknown, which Original Obligors and Assuming Obligors now have by
reason of any cause, matter, or thing through and including the date hereof,
including, without limitation, matters arising out of or relating to: (a) the
Loan, including, without limitation, its funding, administration and servicing;
(b) the Loan Documents; (c) the Property; (d) any reserve and/or escrow balances
held by Lender or any servicers of the Loan; or (e) Transactions, Original
Obligors and Assuming Obligors, on behalf of themselves and their heirs,
successors and assigns, covenant and agree never to institute or cause to be
instituted or continue prosecution of any suit or other form of action or
proceeding of any kind or nature whatsoever against any of the Lender Parties by
reason of or in connection with any of the foregoing matters, claims or causes
of action.

     8. ACKNOWLEDGMENT OF INDEBTEDNESS. This Agreement recognizes the reduction
        -------------------------------
of the principal amount of the Note and the payment of interest thereon to the
extent of payments made by Original Borrower prior to the date of execution of
this Agreement. The parties

                                      -6-

<PAGE>

acknowledge and agree that, as of the date of this Agreement, the principal
balance of the Note is $15,500,000.00 and interest on the Note is paid to August
10, 2006. Assuming Borrower acknowledges and agrees that the Loan, as evidenced
and secured by the Loan Documents, is a valid and existing indebtedness payable
by Assuming Borrower to Lender. The parties acknowledge that Lender is holding
the following escrow and/or reserve balances:

<TABLE>
<S>                       <C>
Tax Escrow:               $21,719.45
Insurance Escrow:         $58,242.81
Replacement Reserve:      $49,022.62
Tenant Improvements and
   Leasing Commissions    $38,396.91
Deferred Maintenance:     $ 9,469.47
</TABLE>

The parties acknowledge and agree that Lender shall continue to hold the escrow
and reserve balances for the benefit of Assuming Borrower in accordance with the
terms of the Loan Documents. Original Obligors covenant and agree that the
Lender Parties have no further duty or obligation of any nature to Original
Obligors relating to such escrow and/or reserve balances. Original Obligors
hereby release and forever discharge the Lender Parties from any obligations to
Original Obligors relating to such escrow and/or reserve balances. Assuming
Obligors acknowledge and agree that the funds listed above constitute all of the
reserve and escrow funds currently held by Lender with respect to the Loan and
authorize such funds to be transferred to an account controlled by Lender for
the benefit of Lender and Assuming Borrower.

The parties further acknowledge and agree that Lender shall direct the Clearing
Bank (as defined in the Cash Management Agreement) to continue to hold and
manage the accounts established pursuant to the Cash Management Agreement for
the benefit of Assuming Borrower in accordance with the terms thereof. Original
Obligors covenant and agree that the Clearing Bank and Lender Parties have no
further duty or obligation of any nature to Original Obligors relating to such
accounts. Original Obligors hereby release and forever discharge the Clearing
Bank and Lender Parties from any obligations to Original Obligors relating to
such accounts.

     9. MODIFICATIONS OF THE LOAN DOCUMENTS. The Loan Documents are hereby
        ------------------------------------
modified as follows:

          (a) Section 34 of the Mortgage is hereby deleted in its entirety and
the following substituted in its stead:

          Section 34. Notices. All notices, demands, requests or other written
                      --------
communications hereunder or required by law shall be in writing and shall be
deemed to have been validly given or served by delivery of the same in person to
the intended addressee, or by depositing the same with a reputable private
courier service for next business day delivery, or by depositing the same in the
United States mail, postage prepaid, registered or certified mail, return
receipt requested, in any event addressed to the intended addressee addressed as
follows:

     If to Borrower:   ARGO Orchard Ridge, LC and
                       Foulger Land Orchard Ridge 2006, LLC

                                      -7-

<PAGE>

                       c/o Columbia Equity Trust, Inc.
                       1750 H Street, NW, Suite 500
                       Washington, DC 20006
                       Attn: Oliver T. Carr, III

     With a copy to:   Hunton & Williams LLP
                       1900 K Street, NW, Suite 1200
                       Washington, DC 20006
                       Attn: John M. Ratino, Esq.

     If to Lender:     Wells Fargo Bank, Minnesota, N.A., as trustee for the
                       registered holders of LB-UBS Commercial Mortgage Trust
                       2004-C4, Commercial Services 2004-C4
                       c/o Wachovia Securities, Commercial Real Estate Services,
                       8739 Research Drive-URP4, Charlotte, NC 28288-1075
                       (28262-1075 for overnight deliveries)
                       Attn: Portfolio Manager

     With a copy to:   Greenberg Traurig LLP
                       1750 Tysons Boulevard, Suite 1200 McLean,
                       Virginia 22102
                       Attn: Marvin W. Ehrlich, Esq.

All notices, demands and requests shall be effective (i) upon delivery, if
delivered in person, (ii) one (1) business day after having been deposited for
overnight delivery with any reputable overnight courier service, or (iii) three
(3) business days after having been deposited in the United States mail as
provided above. Rejection or other refusal to accept or the inability to deliver
because of changed address of which no notice was given as herein required shall
be deemed to be receipt of the notice, demand or request sent. By giving to the
other party hereto at least fifteen (15) days' prior written notice thereof in
accordance with the provisions hereof, the parties hereto shall have the right
from time to time to change their respective addresses and each shall have the
right to specify as its address any other address within the United States of
America."

          (b) Section 13 of the Mortgage is hereby modified by deleting all
references to "Foulger" and replacing them with references to "FOULGER LAND".

          (c) (i) Notwithstanding anything in the Loan Documents to the
contrary, no consent of the Lender shall be required in connection with the
transfer or issuance of any securities or any direct or indirect interests in
any direct or indirect owner of Assuming Borrower that is publicly traded on a
national exchange in the ordinary course of business (including, without
limitation, Columbia Equity Trust, Inc (the "REIT")) provided that, (y) more
                                             ----
than 50% of the direct or indirect interests in Assuming Borrower continue to be
held by Columbia Equity, LP (the "OP"), and (z) the Board of Trustees, Board of
Managers or Board of Directors, as the case may be, of the REIT immediately
prior to the Transfer shall continue to represent a majority of the surviving
entity's Board of Directors, Board of Managers or Board of Trustees, as the case
may be, after such Transfer and continue to control the direction (either

                                      -8-

<PAGE>

directly or indirectly) of the management and policies of the REIT.

          (ii) Notwithstanding anything in the Loan Documents to the contrary,
no consent of the Lender shall be required in connection with the transfer or
issuance of any securities or direct or indirect interests in the OP so long as,
after such event, the REIT shall continue to remain the sole general partner or
the sole managing general partner of the OP, regardless of the percentage of
equity interest in the OP owned by REIT.

     (d) Section 6(c) of the Mortgage is hereby modified by inserting "or
renewal of existing Leases" after "Leases" on line 9.

     (e) Sections 6(d), 6(e), 6(f), 6(g) and 6(h) are hereby deleted.

     (f) Sections 10(hh) of the Mortgage is hereby modified by deleting "dated
December 1, 2000 as amended and assigned through the date hereof ("Management
Agreement") between Trustor and FP-Argo Management II, LC, a Maryland limited
liability company ("Manager") beginning on line 1 and inserting dated August 31,
2006 (the "Management Agreement") between Trustor and Columbia Equity Services,
LLC, a Virginia limited liability company ("Manager") in its place.

     (g) Sections 11(a) (i) of the Note is hereby modified by deleting "the
origination of the Loan" and inserting "the assumption of the Loan" and
inserting at the end of the subsection "provided that Maker shall not be
responsible under this subsection for events which arose or first occurred prior
to the Assumption or under Section 14(h) of this Agreement."

     (h) Section 11(c) of the Note is hereby modified to add the following to
the end thereof: "provided that no individual shareholder of the REIT holding
less than a 10% interest shall be considered a Related Party."

     (i) Section 1(a) (i) of the Indemnity Agreement is hereby modified by
deleting "the origination of the Loan" beginning on Line 4 and inserting "the
assumption of the Loan" and inserting at the end of the subsection "provided
that Assuming Indemnitor shall not be responsible under this subsection for
events which arose or first occurred prior to the Assumption or under Section
14(h) of this Agreement."

     (j) Section 1(c) (F) of the Indemnity Agreement is hereby modified to add
the following to the end thereof: "provided that no individual shareholder of
the REIT holding less than a 10% interest shall be considered a Related Party."

     10. INTEREST ACCRUAL RATE AND MONTHLY INSTALLMENT PAYMENT AMOUNT TO REMAIN
         ----------------------------------------------------------------------
THE SAME. The interest rate and the monthly payments set forth in the Note shall
---------
remain unchanged. Prior to the occurrence of an Event of Default hereunder or
under the Note, interest shall accrue on the principal balance outstanding from
time to time at the Interest Rate (as defined in the Note) and principal and
interest (which does not include such amounts as may be required to fund escrow
obligations under the terms of the Loan Documents) shall continue to be paid in
accordance with the provisions of the Note.

                                      -9-

<PAGE>

     11. CONDITIONS. This Agreement shall be of no force and effect until each
         -----------
of the following conditions has been met to the complete satisfaction of Lender:

          (a) Fees and Expenses. Original Borrower and/or Assuming Borrower
              ------------------
shall pay, or cause to be paid at closing: (i) all costs and expenses incident
to the preparation, execution and recordation hereof and the consummation of the
transaction contemplated hereby, including, but not limited to, recording fees,
filing fees, surveyor fees, broker fees, transfer or mortgage taxes, rating
agency confirmation fees, application fees, all third party fees, search fees,
transfer fees, inspection fees, title insurance policy or endorsement premiums
or other charges of the title company and escrow agent, and the fees and
expenses of legal counsel to any Lender Party and any applicable rating agency
and (ii) an assumption fee to Lender in the amount of $155,000.00 being one
percent (1%) of the outstanding principal balance of the Note as of the date of
the transfer and assumption contemplated by this Agreement, the next regularly
scheduled monthly payment due under the Loan, and the other fees and expenses
outlined in the beneficiary statement distributed to the parties by Lender.

          (b) Other Conditions. Satisfaction of all requirements under the Loan
              -----------------
Documents and the closing checklist for this transaction as determined by Lender
and Lender's counsel in their sole discretion.

     12. DEFAULT.
         --------

          (a) Breach. Any breach of Assuming Obligors or Original Obligors of
              -------
any of the representations, warranties and covenants contained herein shall
constitute a default under the Mortgage and each other Loan Document.

          (b) Failure to Comply. Any failure of Assuming Obligors or Original
              ------------------
Obligors to fulfill any one of the conditions set forth in this Agreement shall
constitute a default under this Agreement and the Loan Documents.

     13. NO FURTHER CONSENTS. Assuming Obligors and Original Obligors
         --------------------
acknowledge and agree that Lender's consent herein contained is expressly
limited to the sale, conveyance, assignment and transfer herein described, that
such consent shall not waive or render unnecessary Lender's consent or approval
of any subsequent sale, conveyance, assignment or transfer of the Property, and
that Section 13 of the Mortgage shall continue in full force and effect, as
modified herein.

     14. ADDITIONAL REPRESENTATIONS, WARRANTIES AND COVENANTS OF ASSUMING
         ----------------------------------------------------------------
OBLIGORS. As a condition of this Agreement, Assuming Obligors represent and
---------
warrant to Lender as follows:

          (a) ARGO is a limited liability company duly organized, validly
existing and in good standing under the laws of the State of Maryland. ARGO has
full power and authority to enter into and carry out the terms of this Agreement
and to assume and carry out the terms of the Loan Documents.

               FOULGER LAND is a limited liability company duly organized,
validly existing and in good standing under the laws of the State of Maryland.
FOULGER LAND has

                                      -10-

<PAGE>

full power and authority to enter into and carry out the terms of this Agreement
and to assume and carry out the terms of the Loan Documents.

          (b) Columbia Orchard Ridge SPE, Inc. is a corporation duly organized
and validly existing in good standing under the laws of the State of Virginia
and is authorized to transact business as a foreign corporation in each
jurisdiction in which such authorization is necessary for the operation of the
business or properties of ARGO. Columbia Orchard Ridge SPE, Inc., is and shall
remain, the Manager of ARGO and has full power and authority to enter into this
Agreement as Manager on behalf of ARGO, and to execute this Agreement.

               101 Orchard Ridge SPE, Inc., is a corporation duly organized and
validly existing in good standing under the laws of the State of Virginia and is
authorized to transact business as a foreign corporation in each jurisdiction in
which such authorization is necessary for the operation of the business or
properties of FOULGER LAND. 101 Orchard Ridge SPE, Inc., is and shall remain,
the Manager of FOULGER LAND and has full power and authority to enter into this
Agreement as Manager on behalf of FOULGER LAND and to execute this Agreement.

          (c) Assuming Indemnitor is a limited partnership duly organized and
validly existing under the laws of the State of Virginia. Assuming Indemnitor
has full power and authority to enter into and carry out the terms of this
Agreement and to assume and carry out the terms of the Loan Documents to which
it is a party.

          (d) This Agreement and the Loan Documents constitute legal, valid and
binding obligations of Assuming Obligors enforceable in accordance with their
respective terms. Neither the entry into nor the assumption and performance of
and compliance with this Agreement or any of the Loan Documents has resulted or
will result in any violation of, or a conflict with or a default under, any
judgment, decree, order, mortgage, indenture, contract, agreement or lease by
which Assuming Obligors or any property of Assuming Obligors are bound or any
statute, rule or regulation applicable to Assuming Obligors.

          (e) There is no action, proceeding or investigation pending or
threatened which questions, directly or indirectly, the validity or
enforceability of this Agreement or any of the other Loan Documents, or any
action taken or to be taken pursuant hereto or thereto, or which might result in
any material adverse change in the condition (financial or otherwise) or
business of Assuming Obligors.

          (f) There has been no legislative action, regulatory change,
revocation of license or right to do business, fire, explosion, flood, drought,
windstorm, earthquake, accident, other casualty or act of God, labor trouble,
riot, civil commotion, condemnation or other action or event which has had any
material adverse effect, on the business or condition (financial or otherwise)
of Assuming Obligors or any of their properties or assets, whether insured
against or not, since Assuming Obligors submitted to Lender their request to
assume the Loan.

          (g) The financial statements and other data and information supplied
by Assuming Obligors in connection with Assuming Obligors' request to assume the
Loan or otherwise supplied in contemplation of the assumption of the Loan by
Assuming Obligors were

                                      -11-

<PAGE>

in all material respects true and correct on the dates they were supplied, and
since their dates no material adverse change in the financial condition of
Assuming Obligors has occurred, and there is not any pending or threatened
litigation or proceedings which might impair to a material extent the business
or financial condition of Assuming Obligors.

          (h) Without limiting the generality of the assumption of the Loan
Documents by Assuming Obligors, Assuming Obligors hereby specifically remake and
reaffirm the representations, warranties and covenants set forth in the Loan
Documents to which they are a party.

          (i) No representation or warranty of Assuming Obligors made in this
Agreement contains any untrue statement of material fact or omits to state a
material fact necessary in order to make such representations and warranties not
misleading in light of the circumstances under which they are made.

          (j) Assuming Borrower hereby represents and warrants to Lender that
Assuming Borrower will not permit the transfer of any interest in Assuming
Borrower to any person or entity (or any beneficial owner of such entity) who is
listed on the specifically Designated Nationals and Blocked Persons List
maintained by the Office of Foreign Asset Control, Department of the Treasury
pursuant to Executive Order No. 13224, 66 Fed. Reg. 49079 (Sept. 25, 2001)
and/or any other list of terrorists or terrorist organizations maintained
pursuant to any of the rules and regulations of Office of Foreign Asset Control,
Department of the Treasury or pursuant to any other applicable Executive Orders
(such lists are collectively referred to as the "OFAC Lists"). Assuming Borrower
will not knowingly enter into a lease with any party who is listed on the OFAC
Lists. Assuming Borrower shall immediately notify Lender if Assuming Borrower
has knowledge that any member or beneficial owner of Assuming Borrower is listed
on the OFAC Lists or (A) is indicted on or (B) arraigned and held over on
charges involving money laundering or predicate crimes to money laundering.
Assuming Borrower shall immediately notify Lender if Assuming Borrower knows
that any tenant is listed on the OFAC Lists or (A) is convicted on, (B) pleads
nolo contendere to, (C) is indicted on or (D) is arraigned and held over on
charges involving money laundering or predicate crimes to money laundering.
Assuming Borrower further represents and warrants to Lender that Assuming
Borrower is currently not on the OFAC List. None of the Assuming Borrower, any
subsidiary of the Assuming Borrower or any affiliate of the Assuming Borrower or
Assuming Indemnitor is (i) named on the list of Specially Designated Nationals
or Blocked Persons maintained by the U.S. Department of the Treasury's Office of
Foreign Assets Control available at
http://www.treas.gov/offices/eotffc/ofac/sdn/index.html, or (ii) (A) an agency
--------------------------------------------------------
of the government of a country, (B) an organization controlled by a country, or
(C) a person residing in a country that is subject to a sanctions program
identified on the list maintained by the U.S. Department of the Treasury's
Office of Foreign Assets Control and available at
http://www.treas.gov/offices/eotffc/ofac/sanctions/index.html, or as otherwise
--------------------------------------------------------------
published from time to time, as such program may be applicable to such agency,
organization or person.

     15. ADDITIONAL REPRESENTATIONS, WARRANTIES AND COVENANTS OF ORIGINAL
         ----------------------------------------------------------------
OBLIGORS. As a condition of this Agreement, Original Obligors represent and
---------
warrant to Lender as follows:

          (a) ARGO Orchard Ridge, LC, is a limited liability company duly
organized,

                                      -12-

<PAGE>

validly existing and in good standing under the laws of the State of Maryland.
Assuming Borrower has full power and authority to enter into and carry out the
terms of this Agreement and to assume and carry out the terms of the Loan
Documents.

               Foulger Land Limited Partnership, is a limited partnership duly
organized, validly existing and in good standing under the laws of the State of
Virginia. Assuming Borrower has full power and authority to enter into and carry
out the terms of this Agreement and to assume and carry out the terms of the
Loan Documents.

          (b) Argo Orchard Ridge Manager, Inc., is a corporation duly organized
and validly existing in good standing under the laws of the State of Maryland
and is authorized to transact business as a foreign corporation in each
jurisdiction in which such authorization is necessary for the operation of the
business or properties of ARGO Orchard Ridge, LC. Argo Columbia Orchard Ridge
SPE, Inc., is and shall remain, the Manager of ARGO Orchard Ridge, LC, and has
full power and authority to enter into this Agreement as Manager on behalf of
ARGO Orchard Ridge, LC, and to execute this Agreement.

               Sid Foulger and Mary Frances Flint Foulger are residents of the
State of Maryland, and are and shall remain, the General Partners of Foulger
Land Limited Partnership, and are legally competent to enter into and execute
this Agreement as General Partners on behalf of Foulger Land Limited
Partnership.

          (c) This Agreement, the Sales Agreement and all other documents
executed by Original Obligors in connection therewith, constitute legal, valid
and binding obligations of Original Obligors enforceable in accordance with
their respective terms. Neither the entry into nor the performance of and
compliance with this Agreement, the Sales Agreement and all other documents
executed by Original Obligors in connection therewith has resulted or will
result in any violation of, or a conflict with or a default under, any judgment,
decree, order, mortgage, indenture, contract, agreement or lease by which
Original Obligors or any property of Original Obligors are bound or any statute,
rule or regulation applicable to Original Obligors.

          (d) Original Obligors have not received any written notices from any
governmental entity claiming that either the Property or Original Obligors' use
of the Property is not presently in compliance with any laws, ordinances, rules,
and regulations bearing upon the use and operation of the Property, including,
without limitation, any notice relating to zoning laws or building code
regulations.

          (e) The certified rent roll provided to Lender of even date herewith,
is a true, complete and accurate summary of all tenant leases ("TENANT LEASES"
or individually, a "TENANT LEASE") affecting the Property as of the date of this
Agreement. No rent has been prepaid under any Tenant Lease except rent for the
current month. Each Tenant Lease has been duly executed and delivered by, and,
to the knowledge of Original Obligors, is a binding obligation of, the
respective tenant, and each Tenant Lease is in full force and effect. Each
Tenant Lease represents the entire agreement between the Original Borrower and
the respective tenant and no Tenant Lease has been terminated, renewed, amended,
modified or otherwise changed without the prior written consent of Lender to the
extent required by the Loan Documents. The tenant under each Tenant Lease has
taken possession of and is in occupancy of the premises therein

                                      -13-
<PAGE>

described and is open for business. Rent payments have commenced under each
Tenant Lease, and all tenant improvements in such premises and other conditions
to occupancy and/or rent commencement have been completed by Original Borrower
or its predecessor in interest. All obligations of the landlord under the Tenant
Leases have been performed, and no event has occurred and no condition exists
that, with the giving of notice or lapse of time or both, would constitute a
default by Original Borrower under any Tenant Lease. There are no offsets or
defenses that any tenant has against the full enforcement of any Tenant Lease by
the Original Borrower. Each Tenant Lease is fully and freely assignable by the
Original Borrower without notice to or the consent of the tenant thereunder.

          (f) Original Borrower is the current owner of the Property. There are
no pending or threatened suits, judgments, arbitration proceeding,
administrative claims, executions or other legal or equitable actions or
proceedings against Original Obligors or the Property, any pending or threatened
condemnation or annexation proceedings affecting the Property, any agreements to
convey any portion of the Property, or any rights thereto, that are not
disclosed in this Agreement, including, without limitation, any pending or
threatened administrative claim by any governmental agency.

          (g) Original Borrower has examined the ALTA, As-Built Survey (the
"SURVEY") performed on the Property in connection with the closing of the Loan.
As an inducement for Lender to consent to the Assumption without requiring an
update to the Survey, Original Borrower represents to Lender that (i) there has
been no improvement added at the Property, (ii) there has been no encroachment
made upon the Property, and (iii) no structural alteration has been made to the
Property from the date of the Survey to the date hereof without the Lender's
prior written consent.

          (h) No representation or warranty of Original Obligors made in this
Agreement contains any untrue statement of material fact or omits to state a
material fact necessary in order to make such representations and warranties not
misleading in light of the circumstances under which they are made.

     16. INCORPORATION OF RECITALS. Each of the Recitals set forth above in this
         --------------------------
Agreement are incorporated herein and made a part hereof.

     17. PROPERTY REMAINS AS SECURITY FOR LENDER. All of the Property shall
         ----------------------------------------
remain in all respects subject to the lien, charge or encumbrance of the
Mortgage. Except as expressly set forth in this Agreement, nothing contained
herein shall affect or be construed to release or affect the liability of any
party or parties who may now or hereafter be liable under or on account of the
Note or the Mortgage, nor shall anything contained herein affect or be construed
to affect any other security for the Note held by Lender.

     18. NO WAIVER BY LENDER. Nothing contained herein shall be deemed a waiver
         --------------------
of any of Lender's rights or remedies under any of the Loan Documents, or under
applicable law.

     19. REFERENCES. From and after the date hereof: (a) references in any of
         -----------
the Loan Documents to any of the other Loan Documents will be deemed to be
references to such other Loan Documents as modified by this Agreement; (b)
references in the Loan Documents to

                                      -14-

<PAGE>

"Borrower" or "Trustor" shall hereafter be deemed to refer to Assuming Borrower;
(c) references in the Loan Documents to the "Guarantor", "Indemnitor" or
"Principal" shall hereafter be deemed to refer to Assuming Indemnitor; and (d)
all references to the term "Loan Documents" or "Security Documents" in the
Mortgage and Assignment shall hereinafter refer to the Loan Documents as defined
herein, this Agreement, and all documents executed in connection with this
Agreement.

     20. RELATIONSHIP WITH LOAN DOCUMENTS. To the extent that this Agreement is
         ---------------------------------
inconsistent with the Loan Documents, this Agreement will control and the Loan
Documents will be deemed amended by this Agreement. Except as explicitly amended
hereby, the Loan Documents shall remain unchanged and in full force and effect.

     21. TITLES AND CAPTIONS. Titles and captions of sections and subsections of
         --------------------
this Agreement have been inserted for convenience only, and neither limit nor
amplify the provisions of this Agreement.

     22. PARTIAL INVALIDITY. Any provision of this Agreement or the Loan
         -------------------
Documents held to be illegal, invalid or unenforceable in any jurisdiction,
shall, as to such jurisdiction, be ineffective only to the extent of such
illegality, invalidity or unenforceability, without invalidating the remainder
of such provision or the remaining provision hereof or thereof or affecting the
legality, validity or enforceability of such provision in any other
jurisdiction.

     23. ENTIRE AGREEMENT. This Agreement and the documents contemplated to be
         -----------------
executed herewith constitute the entire agreement among the parties hereto with
respect to the assumption of the Loan. The Agreement supersedes all prior
negotiations regarding the transfer of the Property and the Assumption. This
Agreement and the Loan Documents may only be amended, revised, waived,
discharged, released or terminated by a written instrument executed by the party
against which enforcement of the amendment, revision, waiver, discharge, release
or termination is asserted. Any alleged amendment, revision, waiver, discharge,
release or termination of this Agreement which is not in writing and signed by
the parties shall not be effective as to any party.

     24. BINDING EFFECT. This Agreement and the documents contemplated to be
         ---------------
executed in connection herewith shall be binding upon and inure to the benefit
of the parties hereto and their respective successors and assigns; provided,
however, that the foregoing provision shall not be a consent by Lender to any
further sale, conveyance, assignment or transfer of the Property by Assuming
Borrower.

     25. MULTIPLE COUNTERPARTS. This Agreement may be executed in multiple
         ----------------------
counterparts, each of which when so executed shall be deemed an original and
shall be binding upon all parties and all of which, taken together, shall
constitute one and the same Agreement.

     26. GOVERNING LAW. This Agreement shall be governed by and construed in
         --------------
accordance with the laws of the State where the Property is located.

     27. EFFECTIVE DATE. This Agreement shall be effective as of the date of its
         ---------------
execution by the parties hereto and upon such date this Agreement shall be
incorporated into the terms of the Loan Documents.

                                      -15-

<PAGE>

     28. TIME OF ESSENCE. Time is of the essence with respect to all provisions
         ----------------
of this Agreement.

     29. CUMULATIVE REMEDIES. All remedies contained in this Agreement are
         --------------------
cumulative and Lender shall also have all other remedies provided at law and in
equity contained in the Mortgage and other Loan Documents. Such remedies may be
pursued separately, successively or concurrently at the sole discretion of
Lender and may be exercised in any order and as often as occasion therefor shall
arise.

     30. CONSTRUCTION. Each party hereto acknowledges that it has participated
         -------------
in the negotiation of this Agreement and that no provision shall be construed
against or interpreted to the disadvantage of any party. Assuming Obligors and
Original Obligors have had sufficient time to review this Agreement, have been
represented by legal counsel at all times, have entered into this Agreement
voluntarily and without fraud, duress, undue influence or coercion of any kind.
Lender has not made a representation or warranty to any party except as set
forth in this Agreement.

     31. WAIVER OF JURY TRIAL. ORIGINAL OBLIGORS, ASSUMING OBLIGORS AND LENDER,
         ---------------------
TO THE FULL EXTENT PERMITTED BY LAW, HEREBY KNOWINGLY, INTENTIONALLY AND
VOLUNTARILY, WITH AND UPON THE ADVICE OF COMPETENT COUNSEL, WAIVE, RELINQUISH
AND FOREVER FORGO THE RIGHT TO A TRIAL BY JURY IN ANY ACTION OR PROCEEDING BASED
UPON, ARISING OUT OF, OR IN ANY WAY RELATING TO THE LOAN DOCUMENTS OR THIS
AGREEMENT.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                      -16-

<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed this Agreement to be
effective as of the date first aforesaid.

     ASSUMING
     --------
     BORROWER:                          ARGO ORCHARD RIDGE, LC,
     ---------                          a Maryland limited liability company

                                        By: Columbia Orchard Ridge SPE, Inc.,
                                            a Virginia corporation, its Manager

                                        By: /s/ Oliver T. Carr, III
                                            ------------------------------------
                                            Oliver T. Carr, III
                                            President

                                        FOULGER LAND ORCHARD RIDGE 2006, LLC,
                                        a Maryland limited liability company

                                        By: 101 Orchard Ridge SPE, Inc.,
                                            a Virginia corporation, its Manager

                                        By: /s/ Oliver T. Carr, III
                                            ------------------------------------
                                            Oliver T. Carr, III
                                            President

<PAGE>

ASSUMING INDEMNITOR:                    COLUMBIA EQUITY, LP,
--------------------                    a Virginia limited partnership

                                        By: Columbia Equity Trust, Inc.,
                                            a Maryland corporation,
                                            its General Partner

                                        By: /s/ Oliver T. Carr, III
                                            ------------------------------------
                                            Oliver T. Carr, III
                                            Chief Executive Officer

<PAGE>

ORIGINAL BORROWER:
------------------

                                        ARGO ORCHARD RIDGE, LC,
                                        a Maryland limited liability company

                                        By: Argo Orchard Ridge Manager, Inc.,
                                            a Maryland corporation, its Manager

                                        By: /s/ John Austin
                                            ------------------------------------
                                        Name: John Austin
                                              ----------------------------------
                                        Title: Member
                                               ---------------------------------

                                        FOULGER LAND LIMITED PARTNERSHIP,
                                        a Virginia limited partnership

                                        By: /s/ Bryant F. Foulger
                                            ------------------------------------
                                        Name: Bryant F. Foulger
                                              ----------------------------------
                                        Title: Vice President
                                               ---------------------------------

<PAGE>

ORIGINAL INDEMNITOR:                    /s/ Bryant Foulger
--------------------                    ----------------------------------------
                                        BRYANT FOULGER

                                        /s/ Clayton Foulger
                                        ----------------------------------------
                                        CLAYTON FOULGER

                                        /s/ John Austin
                                        ----------------------------------------
                                        JOHN AUSTIN

                                        /s/ Richard L. Perlmutter
                                        ----------------------------------------
                                        RICHARD L. PERLMUTTER

                                        /s/ Brent Pratt
                                        ----------------------------------------
                                        BRENT PRATT

<PAGE>

LENDER:                                 Wells Fargo Bank, N.A., as trustee for
-------                                 the registered holders of LB-UBS
                                        Commercial Mortgage Trust 2004-C4,
                                        Commercial Pass-Through Certificates,
                                        Series 2004-C4

                                        By: WACHOVIA BANK, NATIONAL ASSOCIATION,
                                            solely in its capacity as Servicer,
                                            as authorized under that certain
                                            Pooling and Servicing Agreement
                                            dated as of May 11, 2004

                                        By: /s/ Matthew Liebler
                                            ------------------------------------
                                        Name: Matthew Liebler
                                              ----------------------------------
                                        Title: Vice President
                                               ---------------------------------

STATE OF NORTH CAROLINA   )
COUNTY OF MECKLENBURG     )

On this 5th day of September 2006, personally appeared before me of WACHOVIA
BANK, NATIONAL ASSOCIATION, acting in its authorized capacity as Servicer for
and on behalf of Wells Fargo Bank, N.A., as trustee for the registered holders
of LB-UBS Commercial Mortgage Trust 2004-C4, Commercial Services 2004-C4, signer
and sealer of the foregoing instrument and acknowledged the same to be his/her
free act and deed and the free act and deed of said entities, before me. He/she
is personally known to me or has produced a driver's license as identification.

                                        /s/ Janet Garner
                                        ----------------------------------------
                                        Notary Public

                                        My commission expires: 3-27-2010

                                        (Notary Seal)

<PAGE>

                                    EXHIBIT A
                                    ---------

                    [TITLE COMPANY TO ATTACH EXHIBIT A LEGAL
                          DESCRIPTION OF THE PROPERTY]

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