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                                                                    EXHIBIT 10.5

                  COMPLETION AND PAYMENT AGREEMENT AND GUARANTY

      THIS COMPLETION AND PAYMENT AGREEMENT AND GUARANTY (this "GUARANTY") is
made as of the 11th day of April, 2006, by LIBERTY PROPERTY LIMITED PARTNERSHIP,
a Pennsylvania limited partnership (the "INVESTOR A LIMITED PARTNER"), for the
benefit of 1701 JFK BOULEVARD PHILADELPHIA, L.P., a Delaware limited partnership
(the "INVESTOR B LIMITED PARTNER"), and LIBERTY/COMMERZ 1701 JFK BOULEVARD,
L.P., a Delaware limited partnership (the "PARTNERSHIP" and together with the
Investor B Limited Partner, collectively, the "GUARANTEED PARTIES").

                                   WITNESSETH:

      WHEREAS, pursuant to that certain Amended and Restated Limited Partnership
Agreement of the Partnership dated as of the date hereof (the "LP AGREEMENT"),
Liberty Property Philadelphia Corporation IV East, a Pennsylvania corporation
(the "GENERAL PARTNER"), Investor A Limited Partner, and Investor B Limited
Partner reconstituted and continued the Partnership. The General Partner is the
General Partner of the Partnership and the Investor A Limited Partner and
Investor B Limited Partner are the sole other Partners of the Partnership; and

      WHEREAS, the Partnership was formed, reconstituted, and continued for the
purpose of acquiring, financing, and owning, refinancing, leasing, developing,
constructing, and operating, and, if and when appropriate, selling or otherwise
disposing of, the Property. As a condition precedent to and in connection with
the formation of the Partnership and the execution of the LP Agreement, Investor
B Limited Partner has required that the Investor A Limited Partner deliver this
Guaranty unconditionally guaranteeing or paying (as the case may be) to Investor
B Limited Partner and the Partnership, inter alia, the timely lien-free
completion of the Construction Work and the payment and performance of certain
other obligations and undertakings all as more fully described hereinafter;

      NOW, THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, and intending to be legally bound hereby, the Investor A Limited
Partner hereby covenants and agrees as follows:

      1. Unless otherwise set forth in this Guaranty, capitalized terms used
herein shall have the same meaning as set forth in the LP Agreement. For
purposes of this Guaranty, the following terms shall have the following
meanings:

      "ARCH STREET CHURCH CONSTRUCTION AGREEMENT" shall mean that certain
Agreement made as of January 30, 2002 by and among the Partnership, Liberty
Property Philadelphia Limited Partnership IV West, and Arch Street Presbyterian
Church relating to the Property and the property commonly known as 1724 Arch
Street, Philadelphia, Pennsylvania.

      "CERTIFICATE OF FINAL COMPLETION" shall mean a fully executed
certification, in the form of Exhibit F, from the applicable project architect
with respect to the applicable Construction Contract specifying such work has
been completed sufficiently in accordance with the Plans and Specifications
addressed to the Partnership and the Investor B Limited Partner.

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      "COMCAST" shall mean Comcast Corporation, a Pennsylvania corporation.

      "COMCAST CENTER PROJECT" shall mean the planning, development and
construction of the Building, the Concourse, the Public Plaza, the Comcast Lease
Tenant Improvements, the planning, development and construction work required by
the Arch Street Church Construction Agreement, the planning, development and
construction work required by the SEPTA Construction Agreement, in each case in
accordance with all legal requirements and sufficiently in accordance with the
Plans and Specifications such that the Partnership shall receive a Certificate
of Final Completion for each applicable portion of such project. The "Comcast
Center Project" does not include the Non-Comcast Tenant Improvements.

      "COMCAST LEASE TENANT IMPROVEMENTS" shall mean the tenant improvement work
required to be completed pursuant to the Comcast Lease.

      [The confidential material contained herein has been omitted and has been
separately filed with the Commission.].

      "COMPLETION OF THE BUILDING" shall mean "Substantial Completion of
Landlord's Work" as defined in the Comcast Lease.

      "COMPLETION" shall mean completion of such work component sufficiently, as
used with respect to any component of the Construction Work, such that the
Partnership shall receive a Certificate of Final Completion for each such
component, provided, however, if such Certificate of Final Completion refers to
a punch-list of incomplete work items, the issuance of such Certificate shall
not relieve the Investor A Limited Partner from its obligations to complete all
such punch-list items to the satisfaction of the project architect who issued
such Certificate of Final Completion provided however that with respect to
Tenant Improvements the obligations of the Investor A Limited Partner with
respect to such Construction Work shall be deemed satisfied by the issuance of
an estoppel certificate from the relevant tenant certifying that the relevant
Tenant Improvements have been accepted by such tenant and if such estoppel
refers to a punch-list of incomplete work items, the issuance of the estoppel
shall not relieve the Investor A Limited Partner from its obligations to
complete all the punch-list items to the satisfaction of the tenant.

      "CONCOURSE" shall mean that certain concourse level of the Property
connecting the Building to Suburban Station which is to be constructed in
accordance with all legal requirements.

      "CONSTRUCTION AGREEMENT" and "CONSTRUCTION AGREEMENTS" shall mean,
individually and collectively, as the context may require, the Arch Street
Church Construction Agreement and the SEPTA Construction Agreement, as amended
from time to time in accordance with the LP Agreement.

      "CONSTRUCTION CONTRACTS" shall mean, collectively, the contracts entered
into from time to time by the Partnership for the Construction Work in
accordance with the Plans and Specifications, as amended from time to time in
accordance with the LP Agreement. The list of Construction Contracts existing as
of the date hereof is set forth on Exhibit A attached hereto. To the extent
Construction Contracts are entered into after the date hereof, they shall be
added to the list set forth on Exhibit A and become a part hereof.

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      "CONSTRUCTION DOCUMENTS" shall mean, collectively, the Construction
Agreements and the Construction Contracts.

      "CONSTRUCTION WORK" shall mean the entire work required for (a) the
Comcast Center Project (including, without limitation, connection to public
utilities) and (b) the Non-Comcast Tenant Improvements to be performed in
accordance with the applicable Leases and all legal requirements.

      "EASTDIL ARGUS RUN" shall mean that certain "Argus Run" produced by
Eastdil Realty, a summary of which is attached hereto as Exhibit B.

      "EVENT OF DEFAULT" shall mean any failure of the Investor A Limited
Partner to duly perform any of the Obligations under this Guaranty and, to the
extent set forth in Section 15 hereof, after notice of such default and
expiration of the cure period set forth therein.

      "EXCLUDED EXPENSES" shall mean those items set forth on Exhibit E attached
hereto.

      "EXISTING LEASES" shall have the meaning set forth in the NOI Support
Agreement.

      "FINAL OCCUPANCY DATE FOR THE INITIAL OFFICE PREMISES" shall have the
meaning set forth in the Comcast Lease.

      "FORCE MAJEURE" shall mean strikes, lockouts or other labor or industrial
disturbances (whether or not on the part of the employees of the party claiming
the benefit of Force Majeure or Force Majeure Delay), civil disturbance, war,
acts of terrorism, riot, embargo, fire, explosion, inability to secure customary
supplies, materials or labor through ordinary sources, without
reasonably-available and commercially acceptable substitute; lightning,
earthquake, severe storm, hurricane, tornado, flood, and any other causes beyond
the reasonable control of the party from whom performance is required, or any of
its contractors or other representatives; provided, however, that in no event
shall Force Majeure include strikes, walkouts or other labor disturbances in the
event that the party claiming the benefit of Force Majeure or Force Majeure
Delay, or any of its agents or affiliates, materially contributed to or provoked
such strike, lockout or other labor disturbance by violating a labor contract,
collective bargaining agreement or any federal or state labor law or by creating
or approving a lockout. Any prevention, delay or stoppage due to Force Majeure
shall excuse the performance of the party affected for a period of time equal to
the Force Majeure Delay, provided that Force Majeure Delay affecting the paying
party shall not excuse any obligation to pay any other sum of money by either
party on the due date thereof. Each party shall notify the other with reasonable
promptness and shall make reasonable efforts to mitigate the delay so caused.

      "FORCE MAJEURE DELAY" shall mean any actual delay due to Force Majeure
[The confidential material contained herein has been omitted and has been
separately filed with the Commission.].

      "LIEN" and "LIENS" shall mean individually and collectively, as the
context may require, any mortgage, pledge, hypothecation, assignment, deposit
arrangement, encumbrance, lien (statutory or otherwise), preference, priority or
other security agreement or preferential arrangement of any kind or nature
whatsoever (including, without limitation, any conditional sale

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or other title retention agreement, the filing of any financing statement under
the UCC or comparable law of any jurisdiction in respect of any of the foregoing
and a mechanics' or materialmen's lien).

      "NEW INITIAL LEASE" and "NEW INITIAL LEASES" shall mean individually and
collectively, as the context may require, any initial Lease for space that is
currently vacant in the Building by a qualifying tenant pursuant to the Leasing
Guidelines unless otherwise approved by the Investor B Limited Partner.

      "NON-COMCAST TENANT IMPROVEMENTS" shall mean all Tenant Improvements
except the Comcast Lease Tenant Improvements."

      "PERMITTED ENCUMBRANCE" means only those exceptions shown in that certain
Owner's Title Insurance Policy issued in favor of the Partnership by
Commonwealth Land Title Insurance Company as of the date of this Agreement and
each other lien encumbering the Property which has been approved in writing by
the Investor B Limited Partnership set forth on Exhibit C attached hereto.

      "PLANS AND SPECIFICATIONS" means the Plans and Specifications for the
Construction Work as listed on Exhibit D attached hereto and as amended from
time to time in accordance with the LP Agreement.

      "PROJECTED SQUARE FOOTAGE" shall mean 1,254,000 rentable square feet.

      "PUBLIC PLAZA" shall mean that certain public open area and glass enclosed
"winter garden" intended to serve as an entranceway to the Concourse and to
Suburban Station, and known as Unit 3 and Unit 3A under the Condominium
Declaration, which is to be constructed in accordance with all legal
requirements and sufficiently in accordance with the Plans and Specifications
such that the Partnership shall receive a Certificate of Final Completion with
respect to the Construction Work relating to the Public Plaza.

      "REDEVELOPMENT ASSISTANCE CAPITAL PROGRAM GRANT" shall mean that certain
grant issued and funded by the Commonwealth of Pennsylvania, acting through the
Office of the Budget, to the Philadelphia Authority for Industrial Development
in the amount of $30,000,000 for the development of the Public Plaza to be paid
out to the Partnership on a reimbursement basis during the construction of the
Public Plaza.

      "REQUIRED PARKING" means the [The confidential material contained herein
has been omitted and has been separately filed with the Commission.] parking
spaces to be included in the Building.

      "SEPTA" shall mean the Southeastern Pennsylvania Transportation Authority,
an agency and instrumentality of the Commonwealth of Pennsylvania.

      "SEPTA CONSTRUCTION AGREEMENT" shall mean that certain Construction
Agreement made as of August 8, 2001 by and among the Partnership, Liberty
Property Philadelphia Limited Partnership IV West, and SEPTA, relating to the
Property, the Concourse and SEPTA's Suburban Station.

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      "SQUARE FOOTAGE DEVIATION" shall have the meaning set forth in
Section 2(b)(iii).

      "SUBURBAN STATION" shall mean SEPTA's commuter rail station located
adjacent to the Property and commonly known as Suburban Station.

      "TENANT IMPROVEMENTS" shall mean all tenant improvements required to be
performed by the Partnership pursuant to the Existing Leases and New Initial
Leases in accordance with the applicable Leases and all legal requirements.

      "UNREALIZED FINANCING COSTS" means the difference between (i) any
Financing Costs paid by the Partnership based on an Initial Mortgage Loan of
$324,000,000 and (ii) the Financing Costs that would have been paid had the
Financing Costs been calculated based on the reduced principal amount of the
Initial Mortgage Loan resulting from the Square Footage Deviation or failure to
obtain the Required Parking.

      2. (a) The Investor A Limited Partner hereby unconditionally guarantees to
the Investor B Limited Partner, the Partnership and their respective successors
and assigns and hereby agrees to become surety for

            (i) [The confidential material contained herein has been omitted and
has been separately filed with the Commission.]

            (ii) Completion of Tenant Improvements. The full and timely
Completion of the Tenant Improvements.

            (iii) Liens. The prompt discharge of any Lien with respect to the
Construction Work. If any Lien relating to the Construction Work (other than a
Permitted Encumbrance) is filed against the Property, Investor A Limited Partner
shall cause such Liens to be removed or satisfied of record, or cause such Liens
to be bonded over, no later than the earlier of (i) sixty (60) days after notice
thereof to the Investor A Limited Partner (it being acknowledged that any notice
to the Partnership or General Partner shall be considered notice to the Investor
A Limited Partner) or (ii) such other time as may be required pursuant to any
Lease, all to the satisfaction of the Investor B Limited Partner and the
Partnership;

            (iv) LPLP Loan. The full and punctual payment of any amount which
may become due and owing under the LPLP Loan (including debt service and any
amounts due at maturity), in excess of the net proceeds of the Initial Mortgage
Loan and the Initial Capital Contribution of the Investor B Limited Partner
which pursuant to the LP Agreement are to be paid on account of the LPLP Loan.
The obligations of the Investor A Limited Partner pursuant to this paragraph
shall be deemed satisfied upon the issuance of a certificate of LPLP stating
either that the LPLP Loan has been fully paid and satisfied or that LPLP has
assumed any outstanding balance of all principal, interest and other sums owing
under the LPLP Loan and irrevocably agrees to indemnify and hold the Partnership
and the Investor B Limited Partner harmless for any sums owing under the LPLP
Loan; and

            (v) Construction Documents. Full performance of all obligations of
the Partnership set forth in each of the Construction Documents.

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      (b) The Investor A Limited Partner hereby agrees to:

            (i) Completion of Tenant Improvements. Pay to the Partnership and
cause the Partnership to pay to each tenant, contractor, vendor, and/or other
applicable third party (including, without limitation, the prompt payment of all
sums due to contractors, architects, project managers, consultants,
subcontractors, suppliers, furnishers, laborers, surveyors, engineers, public
authorities, and adjacent property owners) all costs and expenses relating to
the full and timely Completion of the Tenant Improvements as and when due in
accordance with the requirements of each applicable Lease. In addition, the
Investor A Limited Partner shall pay to the Partnership any reduction in rent
pursuant to any Existing Lease or New Initial Lease as a result of any unused
tenant allowance for such applicable Tenant Improvements within five (5) days of
the effective date of such rent reduction;

            (ii) Construction Work. Pay to the Partnership and cause the
Partnership to make full and punctual payment to each tenant, contractor,
vendor, and/or other applicable third party (including, without limitation, the
prompt payment of all sums due to contractors, architects, project managers,
consultants, subcontractors, suppliers, furnishers, laborers, surveyors,
engineers, public authorities, and adjacent property owners) for all costs and
expenses relating to Completion of the Construction Work;

            (iii) Square Footage Deviation. If upon Completion of the Building,
the rentable square footage of the Building (as measured pursuant to Section
2(e) of the Comcast Lease) is [The confidential material contained herein has
been omitted and has been separately filed with the Commission.] percent ([The
confidential material contained herein has been omitted and has been separately
filed with the Commission.]%) or more lower than the Projected Square Footage
("Square Footage Deviation"), pay to the Partnership and cause the Partnership
to pay to the Investor B Limited Partner or any tenant, as applicable, within
the earlier of fifteen(15) days of such determination or, in the case of clause
(B) herein below, such time period required pursuant to any applicable Lease, an
amount equal to (A) the equivalent of the weighted average of net rents
identified in the tenant roster of the Eastdil Argus Run (for all tenants other
than Comcast) multiplied by an amount equivalent to the balance of the Projected
Square Footage less the actual square footage and divided by [The confidential
material contained herein has been omitted and has been separately filed with
the Commission.]%, which payment shall be distributed to Partners of the
Partnership in accordance with their Percentage Interest and constitute a return
of the Partner's Capital Contribution, and (B) without duplication of the
payments in (A) above, any and all obligations (including payment obligations)
arising under any Lease from such reduced square footage of the Building.

            (iv) [The confidential material contained herein has been omitted
and has been separately filed with the Commission.]

            (v) LPLP Loan. Subject to Section 2(a)(iv), pay to the Partnership
in sufficient time in order for the Partnership to be able to make timely
payment of each applicable LPLP Loan payment on or prior to each applicable LPLP
Loan payment date and to cause the Partnership to pay as and when due any amount
which may become due and owing under the LPLP Loan (including debt service and
any amounts due at maturity) and to cause the LPLP Loan to be satisfied in full
upon the funding of the Initial Mortgage Loan;

                                      -6-
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            (vi) Initial Tenant Costs. Pay to the Partnership and cause the
Partnership to pay to each tenant, broker, contractor, vendor or other
applicable third party as and when due all Initial Tenant Costs including,
without limitation, any payments due Comcast pursuant to Section 53 of the
Comcast Lease;

            (vii) Late TI Delivery and Late Delivery under Comcast Lease. Pay to
the Partnership and cause the Partnership to pay to each applicable tenant as
and when due all costs, fees, losses (including, without limitation, any
reduction in rent) and expenses that may arise under any Existing Lease or New
Initial Lease as a result of any delay in delivering such leased space complete
as of the applicable delivery date (including, without limitation, late delivery
of the "Base Project Work" or "Tenant Work" under the Comcast Lease);

            (viii) Initial Mortgage Loan. Pay to the Partnership and cause the
Partnership to pay to the Initial Mortgage Lender on behalf of the Partnership
as and when due any costs, fees, losses and expenses (including without
limitation increases in interest, breakage costs, and Hedging Costs (as defined
in the Rate Lock Agreement) incurred pursuant to the Rate Lock Agreement)
arising in connection with the Initial Mortgage Loan (or termination of the
Commitment Letter) as a result of (A) a failure to achieve (I) Final Occupancy
for the Initial Office Premises on or before [The confidential material
contained herein has been omitted and has been separately filed with the
Commission.]or (II) completion of the "Office Tower Work, Plaza Work and Church
Work" as described in Section 3(ff) of the Commitment Letter on or before [The
confidential material contained herein has been omitted and has been separately
filed with the Commission.], (B) a failure to satisfy the provisions of Sections
3(ee)(ii)-(v) of the Commitment Letter on or before [The confidential material
contained herein has been omitted and has been separately filed with the
Commission.] or (C) a Liberty Related Loan Termination.

            (ix) Pre-Completion Return. Pay to the Partnership any amounts
necessary in sufficient time to enable the Partnership to pay the Pre-Completion
Return to the Investor B Limited Partner as and when due to the Investor B
Limited Partner pursuant to the LP Agreement and to cause the Partnership to pay
the Pre-Completion Return in accordance with the terms and conditions of the LP
Agreement;

            (x) [The confidential material contained herein has been omitted and
has been separately filed with the Commission.]

            (xi) [The confidential material contained herein has been omitted
and has been separately filed with the Commission.]

            (xii) Payment of Partnership Liabilities. Subject to Section 13, pay
to the Partnership and cause the Partnership to pay to each applicable obligee
as and when due all liabilities and expenses of the Partnership except Excluded
Expenses arising in or related to the period of time prior to the Transition
Date such that with respect to the period of time prior to the Transition Date
the Investor B Limited Partner shall not be required or obligated to pay any
amounts other than the payment of its Initial Capital Contribution and pro rata
share of Partnership Closing Costs and Excluded Expenses.

                                      -7-
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            (xiii) Unrealized Financing Costs. Promptly pay to the Partnership
any Unrealized Financing Costs.

            (xiv) Negative Carry. Upon receipt of a refund of any Negative Carry
promptly pay eighty percent (80%) of such amounts to the Partnership and cause
the Partnership to pay such amounts to the Investor B Limited Partner.

        (c) Costs and Expenses. The Investor A Limited Partner hereby agrees to
pay to the Guaranteed Parties all costs, fees, losses, and expenses, arising as
a result of any of the items under Subsections 2(a) and 2(b) above not occurring
by the relevant dates.

      Each of the guaranteed undertakings pursuant to Section 2(a) through (c)
is hereinafter referred to as an "OBLIGATION," and collectively, the
"OBLIGATIONS."

      3. For purposes of clarification and the avoidance of doubt, until the
funding of the Initial Mortgage Loan the Investor A Limited Partner may advance
amounts under the LPLP Loan in order to comply with its Obligations under this
Guaranty, provided, however, after the funding of the Initial Mortgage Loan any
payments made by the Investor A Limited Partner in order to comply with its
Obligations under this Guaranty shall not be treated as an advance of amounts
under the LPLP Loan.

      4. Upon an Event of Default hereunder, the Investor B Limited Partner
and/or the Partnership shall be entitled to all rights and remedies available
hereunder and at law or in equity (subject to Section 6 below), and furthermore
the Investor B Limited Partner and/or the Partnership are hereby authorized to
set off and apply any indebtedness at any time, without notice to the Investor A
Limited Partner, held or owing by either the Investor B Limited Partner or the
Partnership to or for the credit or the account of the Investor A Limited
Partner against the Obligations hereunder. The Investor B Limited Partner shall
endeavor to provide notice of any such setoff to the Investor A Limited Partner
promptly after the setoff is made.

      5. The Investor A Limited Partner acknowledges and agrees that it may be
impossible to accurately measure the damages to the Investor B Limited Partner
and/or the Partnership resulting from a breach of the Investor A Limited
Partner's covenants under Section 2 (subject to Section 6), that such breach may
cause irreparable injury to the Investor B Limited Partner and the Partnership,
and that the Investor B Limited Partner and the Partnership may have no adequate
remedy at law in respect of such breach; therefore, the Investor A Limited
Partner agrees that such covenant shall be specifically enforceable against it.
This Section shall not prejudice the right of the Investor B Limited Partner
and/or the Partnership to assert any and all claims for damages incurred as a
result of a default by the Investor A Limited Partner hereunder.

      6. [The confidential material contained herein has been omitted and has
been separately filed with the Commission.]

      7. The Investor A Limited Partner hereby waives any legal requirements
that upon an Event of Default either the Investor B Limited Partner, the
Partnership or both make any demand upon, or institute any action or proceedings
at law or in equity against any other person or entity as a condition precedent
to bringing an action against the Investor A Limited Partner based on this
Guaranty. In connection with any such action or proceeding, the Investor A
Limited Partner

                                      -8-
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waives any right to any stay of execution. All remedies, whether exercised by
the Investor B Limited Partner and/or the Partnership or not, shall not be
deemed to be an exclusion of any of the other remedies available to the Investor
B Limited Partner and/or the Partnership or limit or prejudice any other legal
or equitable remedy which the Investor B Limited Partner and/or the Partnership
may have, subject to the terms of Section 6 hereof. This Guaranty, to the extent
applicable, shall be deemed an agreement of suretyship under the laws of the
State of Delaware.

      8. This Guaranty shall remain in full force and effect and will be
discharged only if and when the Obligations have been fully performed; provided,
however, that notwithstanding any of the foregoing to the contrary, this
Guaranty shall remain in full force and effect for so long as any payment
hereunder may be voided in bankruptcy proceedings as a preference or for any
other reason. Until the satisfaction of the Obligations and the full performance
of the terms, covenants and conditions of this Guaranty or unless (and only to
the extent) the Investor B Limited Partner and the Partnership may otherwise
agree in writing, the Investor A Limited Partner shall not be released from its
Obligations hereunder (a) by any act or circumstance which might, but for this
Section, be deemed a legal or equitable discharge of a guarantor or surety other
than performance in full of the Obligations, or (b) by reason of any waiver,
extension, modification, forbearance or delay by the Investor B Limited Partner
or the Partnership in exercising any right described herein or with respect to
any Lease or otherwise available to the Investor B Limited Partner or the
Partnership or other act or omission of the such party or the failure of such
party to proceed promptly or otherwise, or (c) by reason of any action taken or
omitted by any person or entity other than the Investor B Limited Partner or
circumstance which might vary the risk or affect the rights or remedies of the
Investor A Limited Partner, or (d) by reason of any further dealings between the
Partnership and the Investor A Limited Partner, whether relating to the Property
or otherwise. The Investor A Limited Partner hereby expressly waives and
surrenders any defenses to its liability hereunder based upon any of the
foregoing acts, omissions, agreements or waivers of the Investor B Limited
Partner and/or the Partnership, it being the purpose and intent of the parties
hereto that the Obligations of the Investor A Limited Partner hereunder are
absolute and unconditional.

      9. The liability of the Investor A Limited Partner shall not be deemed to
be waived, released, discharged, impaired or affected by reason of the release
or discharge of the Partnership or any assignee in any condition, receivership,
bankruptcy proceedings or other reorganization proceedings under the Bankruptcy
Code or other insolvency proceeding, or the rejection or disaffirmation of the
Partnership or any assignee in any such insolvency proceeding, and shall
continue with respect to all of the Obligations, including without limitation,
all obligations which would have accrued under any Lease absent such rejection
or disaffirmation of any Lease.

      10. The Investor A Limited Partner's liability under this Guaranty is a
guaranty of payment and performance and not of collection. The Investor A
Limited Partner hereby waives notice of acceptance of this Guaranty by the
Investor B Limited Partner and the Partnership and of presentment, demand,
protest, notice of protest and of dishonor, and all other notices (except to the
extent set forth in Section 2 and Section 15 hereof) relative to this Guaranty
now or hereafter provided by any agreement by, between or among the Partnership
and/or the Investor B Limited Partner and any other person or entity or any
statute or rule of law. Notwithstanding anything herein to the contrary, the
Investor A Limited Partner acknowledges and agrees that upon and

                                      -9-
<PAGE>

during the continuance of any failure to perform the Obligations set forth in
Section 2 hereof (including, without limitation, the failure to complete any
item by the applicable due date), and notwithstanding whether there is an Event
of Default, no payments shall be made by the Partnership pursuant to the LPLP
Loan in excess of appropriate hold backs to pay the cost of remedying any such
default, provided that upon closing of the Initial Mortgage Loan the proceeds
thereof may be used to satisfy the LPLP Loan subject to the right of set off
pursuant to Section 6 and the establishment of appropriate holdbacks adequate to
pay the costs of remedying any such defaults by the Investor A Limited Partner
hereunder as determined by the Investor B Limited Partner. Each Guaranteed Party
has the right to require the Investor A Limited Partner to pay, comply with and
satisfy its obligations and liabilities hereunder, and shall have the right to
proceed immediately against the Investor A Limited Partner with respect thereto,
without being required to attempt recovery first from any other party. Interest
at LIBOR plus 600 basis points shall accrue on any judgment obtained by any
Guaranteed Party until such judgment is paid in full.

      11. This Guaranty shall be a continuing, absolute and unconditional
guarantee regardless of the validity, regularity, enforceability or legality of
(a) any of the Obligations, (b) any other guaranty with respect to the
Obligations, or (c) any term of any document evidencing or relating to any of
the Obligations. In the event that for any reason one or more of the provisions
of this Guaranty or their application to any person, entity or circumstance
shall be held to be invalid, illegal or unenforceable in any respect or to any
extent, such provisions shall nevertheless remain valid, legal and enforceable
in all such other respects and to such extent as may be permissible. In
addition, any such invalidity, illegality, or unenforceability shall not affect
any other provision hereof, but this Guaranty shall be construed as if such
invalid, illegal or unenforceable provision had never been contained herein. No
payment by the Investor A Limited Partner shall entitle the Investor A Limited
Partner, by subrogation or otherwise, to any payment from the Partnership or the
Investor B Limited Partner under or out of the property of the Partnership or
the Investor B Limited Partner, including but not limited to the revenues
derived from any Lease or the demised premises under any Lease; provided that
the foregoing shall not be deemed to impact the rights of the Investor A Limited
Partner pursuant to Section 12 below. Any indebtedness of the Partnership to the
Investor A Limited Partner, now or hereafter existing, together with any
interest thereon, shall be subordinated to the prior payment in full and
complete performance of the Obligations; provided, however, payments may be made
by the Partnership pursuant to the LPLP Loan to the extent permitted pursuant to
Section 10 hereof.

      12. Upon request by the Investor A Limited Partner from time to time, the
Investor B Limited Partner shall provide a written certification stating to the
best of the knowledge of Investor B Limited Partner, as of the date of such
certification, which obligations of the Investor A Limited Partner hereunder
have been satisfied and which have not been satisfied. The Investor B Limited
Partner agrees to act in good faith in responding to such a request and shall
issue the requested certification within twenty (20) days of the request. Any
such certification shall be binding on all the Guaranteed Parties.

      13. In consideration for the agreements of the Investor A Limited Partner
set forth herein, provided there exists no Event of Default or if there is an
Event of Default, provided the Investor B Limited Partner has established
holdbacks adequate to pay the costs of remedying any such defaults by the
Investor A Limited Partner and setoffs with respect to such Events of Default,
the Investor A Limited Partner shall be entitled to retain all Project
Development Assets

                                      -10-
<PAGE>

(as defined below), whether received or receivable by the Partnership or the
Investor A Limited Partner, all of which are hereby assigned by the Partnership
to the Investor A Limited Partner, subject to the obligation to pay over to the
Partnership any amounts required to be repaid or refunded to the source of the
funds. If the Partnership or the Investor B Limited Partner shall at any time
receive a Project Development Asset, the party receiving same shall forthwith
remit it and assign it to the Investor A Limited Partner. As used herein,
"PROJECT DEVELOPMENT ASSETS" shall mean: (a) all sources of funds (other than
Capital Contributions) made available to the Partnership for the payment or
reimbursement of the costs of development and construction of the Property,
including without limitation any governmental or quasi-governmental grants or
incentives such as the proceeds of the Redevelopment Assistance Capital Program
Grant, and any payments or contributions from a tenant for tenant improvements
or tenant inducements (subject to the obligation to repay any unused amount to
the tenant under the applicable lease) in connection with the Existing Leases
and the New Initial Leases; (b) all claims, actions, causes of action,
counterclaims and receivables (excluding revenue under Leases and/or payments
under the NOI Support Agreement) of the Partnership relating in any way to the
development, construction and initial leasing of the Property, including without
limitation all such matters against any contractors, subcontractors, suppliers
of equipment or materials, vendors, labor unions, architects, engineers, design
professionals, attorneys and other professionals, neighbors, community groups,
governmental and quasi-governmental agencies, and other public or private third
parties excluding any warranties (express or implied) or claims thereunder
contained in any Construction Document; and (c) the proceeds of any of the
above. The Investor A Limited Partner shall have the unilateral right, in its
sole discretion, to institute, prosecute, appeal, settle and discharge any and
all claims, actions, causes of action and counterclaims referred to above or
arising out of the Project Development Assets, whether in the name of the
Investor A Limited Partner or its Affiliates or in the name of the Partnership,
and the Investor A Limited Partner shall indemnify, defend and hold the
Partnership and the Investor B Limited Partner harmless against all such
matters.

      14. The Investor A Limited Partner individually represents and warrants
that:

            (a) The Investor A Limited Partner has the full power and authority
to execute and deliver this Guaranty and to perform its obligations hereunder.
The Investor A Limited Partner is duly organized, validly existing and in good
standing under the laws of the state of its formation. The execution, delivery
and performance of this Guaranty by the Investor A Limited Partner have been
duly and validly authorized and the person(s) signing this Guaranty on the
Investor A Limited Partner's behalf have been validly authorized and directed to
sign this Guaranty.

            (b) This Guaranty constitutes the Investor A Limited Partner's
legal, valid and binding obligation, enforceable against it in accordance with
its terms, except to the extent enforceability may be limited under applicable
bankruptcy and insolvency laws and similar laws affecting creditors' rights
generally and to general principles of equity.

            (c) The Investor A Limited Partner's execution, delivery and
performance of this Guaranty will not (i) violate the Investor A Limited
Partner's organizational documents, (ii) result in the breach of, or conflict
with, or result in the acceleration of, any obligation under any Guaranty,
indenture, credit facility or other instrument to which the Investor

                                      -11-
<PAGE>

A Limited Partner or any of its assets may be subject, or (iii) violate any
order, judgment or decree to which the Investor A Limited Partner or any of its
assets is subject.

            (d) No action, suit, proceeding or investigation, judicial,
administrative or otherwise (including without limitation any reorganization,
bankruptcy, insolvency or similar proceeding), currently is pending or, to the
best of the Investor A Limited Partner's knowledge, threatened against the
Investor A Limited Partner which, either in any one instance or in the
aggregate, may have a material, adverse effect on the Investor A Limited
Partner's ability to perform its obligations under this Guaranty.

            (e) The Investor A Limited Partner owns a direct interest in the
Partnership and derives substantial benefit from the activities of the
Partnership. The Investor A Limited Partner also acknowledges that the costs
that may be incurred by the Investor A Limited Partner hereunder with respect to
the Obligations may be larger in amount and more burdensome than that of the
Partnership or the Investor B Limited Partner.

            (f) No material, adverse change has occurred in the financial
condition of the Investor A Limited Partner since the date of its most recent
financial statements submitted to the Investor B Limited Partner, other than
that which has been disclosed in writing to the Investor B Limited Partner and
acknowledged in writing by the Investor B Limited Partner.

      15. Except for the Obligations set forth in Section 2(a)(i), a failure of
the Investor A Limited Partner to duly perform any of the Obligations of the
Investor A Limited Partner under this Guaranty shall not constitute an Event of
Default hereunder, and the Guaranteed Parties shall not have the right to
exercise any remedies with respect thereto, unless: (a) with respect to any
payment obligations of the Investor A Limited Partner, such default shall have
continued for a ten (10) day period after written notice shall have been given
to the Investor A Limited Partner by either the Partnership or the Investor B
Limited Partner specifying such default and requiring such default be remedied,
or (b) with respect to any obligation of the Investor A Limited Partner other
than a payment obligation, such default shall have continued for a thirty (30)
day period after written notice shall have been given to the Investor A Limited
Partner by either the Partnership or the Investor B Limited Partner specifying
such default and requiring such default be remedied (or, if such default by its
nature is incapable of being remedied in thirty (30) days, such longer period as
shall be reasonably required to complete such remedy, provided that the Investor
A Limited Partner shall commence actions to remedy such default within thirty
(30) days and continue diligently thereafter to complete the remedy thereof) and
provided further that the Investor A Limited Partner shall notwithstanding any
cure be liable for any losses or damages arising as a result of such default.

      16. Any notice, demand or request hereunder shall be governed by Section
12.01 of the LP Agreement.

      17. This Guaranty shall be binding upon the Investor A Limited Partner,
and upon its successors and assigns, and shall inure to the benefit of the
Investor B Limited Partner and the Partnership and their respective successors
and assigns.

                                      -12-
<PAGE>

      18. No modification of this Guaranty shall be effective unless in writing
and signed by the Investor B Limited Partner and the Partnership and the
Investor A Limited Partner.

      19. This Guaranty shall be construed, enforced, and interpreted according
to the laws of the State of Delaware (without regard to principles of conflicts
of law).

      20. Except as otherwise set forth in Section 6 hereof, the rights and
remedies provided by this Guaranty are cumulative and the use of any one right
or remedy by any party hereto shall not preclude or waive the right to use any
and all other remedies. Such rights and remedies are given in addition to any
other rights the parties hereto may have by law, statute, ordinance or
otherwise, including but not limited to, rights granted under the LP Agreement,
the NOI Support Agreement, the Management and Leasing Agreement and the Master
Agreement.

                       [Signatures on the Following Page]

                                      -13-
<PAGE>

      IN WITNESS WHEREOF, the Investor A Limited Partner has hereunto set its
hand and seal on the date first above written intending to be legally bound
hereby.

                              INVESTOR A LIMITED PARTNER:

                              LIBERTY PROPERTY LIMITED PARTNERSHIP, a
                              Pennsylvania limited partnership

                              By:    Liberty Property Trust, its general partner

                              By:    /s/ William P. Hankowsky
                                     -----------------------------------------
                              Name:  William P. Hankowsky
                              Title: Chairman, President and CEO

                              By:    /s/ George J. Alburger, Jr.
                                     -----------------------------------------
                              Name:  George J. Alburger, Jr.
                              Title: Chief Financial Officer

                                      -14-
<PAGE>

                                    EXHIBIT A

[The confidential material contained herein has been omitted and has been
separately filed with the Commission.]

<PAGE>

                                    EXHIBIT B

[The confidential material contained herein has been omitted and has been
separately filed with the Commission.]

<PAGE>

                                    EXHIBIT C

[The confidential material contained herein has been omitted and has been
separately filed with the Commission.]

<PAGE>

                                    EXHIBIT D

[The confidential material contained herein has been omitted and has been
separately filed with the Commission.]

<PAGE>

                                    EXHIBIT E

[The confidential material contained herein has been omitted and has been
separately filed with the Commission.]

<PAGE>

                                    EXHIBIT F

[The confidential material contained herein has been omitted and has been
separately filed with the Commission.]