<PAGE>   1
                                                                   EXHIBIT 10.4



                               FIRST AMENDMENT TO
                                  $345,000,000
                              AMENDED AND RESTATED
                                CREDIT AGREEMENT




                           DATED AS OF APRIL 14, 2000



                                  BY AND AMONG

                      AIMCO PROPERTIES, L.P., AS BORROWER,

                 BANK OF AMERICA, N.A., AS ADMINISTRATIVE AGENT

                  U.S. BANK NATIONAL ASSOCIATION, AS A LENDER




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                               FIRST AMENDMENT TO
                                  $345,000,000
                     AMENDED AND RESTATED CREDIT AGREEMENT


      This FIRST AMENDMENT TO AMENDED AND RESTATED CREDIT AGREEMENT (this
"AMENDMENT") is dated as of April 14, 2000 (the "AMENDMENT EFFECTIVE DATE") and
entered into by and among AIMCO PROPERTIES, L.P. a Delaware limited partnership
("BORROWER"), BANK OF AMERICA, N.A. ("BANK OF AMERICA"), as Administrative
Agent (in such capacity, "ADMINISTRATIVE AGENT") and U.S. BANK NATIONAL
ASSOCIATION ("U.S. BANK"), as a Lender, and is made with reference to that
certain Credit Agreement dated as of August 16, 1999, as amended by that
certain Amended and Restated Credit Agreement dated as of March 15, 2000 (as
amended by this Amendment, the "CREDIT AGREEMENT"), by and among Borrower,
Lenders and Administrative Agent. Capitalized terms used in this Amendment
shall have the meanings set forth in the Credit Agreement unless otherwise
defined. The Guarantor Subsidiaries set forth on pages S-4 through S-12 are
only parties to this Amendment for purposes of Section 4 and are not a party to
the Credit Agreement.

                                    RECITAL

         WHEREAS, Borrower and Administrative Agent desire to amend the Credit
Agreement to increase the Combined Commitments by $5,000,000 to an aggregate
total of $350,000,000 as of the date hereof;

         WHEREAS, each of the Lenders has acknowledged and agreed that its
consent to any increase in the Combined Commitments up to a maximum of
$400,000,000 is not required so long as Administrative Agent and Borrower have
consented in writing to such increase;

         WHEREAS, U.S. Bank, Administrative Agent and Borrower hereby consent
to the increase in the Commitments of U.S. Bank from $40,000,000 to
$45,000,000;

         NOW, THEREFORE, in consideration of the agreements, provisions and
covenants contained herein, the parties agree as follows:

AMENDMENTS TO THE CREDIT AGREEMENT

AMENDMENT TO SUBSECTION 1.01: DEFINED TERMS.

Subsection 1.01 of the Credit Agreement is hereby further amended by deleting,
in their entirety, the definitions of the terms listed below and inserting the
following in lieu thereof:

                  "COMBINED COMMITMENTS" has the meaning assigned to such term
         in the definition of "Commitment". The Combined Commitments are
         $350,000,000, and are subject to increase in accordance with Section
         2.14.




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                  "PRO RATA SHARE" means, with respect to each Lender, the
         percentage of the Combined Commitments set forth opposite the name of
         that Lender on Schedule 2.01, as may be amended from time to time.

AMENDMENT TO SCHEDULES.

Schedule 2.01 shall be deleted in its entirety and replaced with that attached
hereto.

CONDITIONS TO EFFECTIVENESS

         This Amendment shall become effective on the Amendment Effective Date,
if each of the following conditions are satisfied:

Borrower and U.S. Bank have delivered to Lenders (or to Administrative Agent
for Lenders with sufficient originally executed copies, where appropriate, for
each Lender and its counsel) executed copies of this Amendment dated as of the
Amendment Effective Date;

Guarantor Subsidiaries have executed this Amendment with respect to Section 4;

Borrower shall have executed a new Committed Loan Note for U.S. Bank dated as
of the Amendment Effective Date and in an amount equal to U.S. Bank's
Commitment;

On or before the Amendment Effective Date, Borrower has paid to Administrative
Agent a commitment fee in the amount of $18,750;

Borrower shall have delivered a certificate, satisfactory to Agent, signed
by a Responsible Officer stating that (i) the representations and warranties
contained in Section 5 are true and correct on and as of the Amendment
Effective Date, and (ii) no Default or Event of Default then exists, and no
Default or Event of Default will result from the consummation of the
transactions contemplated by this Amendment;

If required by Administrative Agent, Lenders and their respective counsel
shall have received originally executed copies of one or more favorable written
opinions of counsel for Borrower and the Guarantor Subsidiaries in form and
substance reasonably satisfactory to Administrative Agent and its counsel,
dated as of the Amendment Effective Date, with respect to the validity, binding
effect and enforceability of this Amendment, and due authorization, execution
and delivery thereof, and as to such other matters as Administrative Agent
acting on behalf of Lenders may reasonably request; and

Borrower shall have paid the reasonable fees, costs and expenses of
Administrative Agent's counsel in connection with this Amendment.

BORROWER'S REPRESENTATIONS AND WARRANTIES

                  In order to induce Lenders to enter into this Amendment and
to amend the Credit Agreement in the manner provided herein, Borrower
represents and warrants to each Lender that the following statements are true,
correct and complete:




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CORPORATE POWER AND AUTHORITY. Borrower has all requisite corporate power and
authority to enter into this Amendment and any other agreements, guaranties or
other operative documents to be delivered pursuant to this Amendment, to carry
out the transactions contemplated by, and perform its obligations under, the
Credit Agreement. Each of the Borrower, the REIT and the Guarantor Subsidiaries
are in good standing in the respective states of their organization on the
Amendment Effective Date.

AUTHORIZATION OF AGREEMENTS. The execution and delivery of this Amendment and
the performance of the Credit Agreement have been duly authorized by all
necessary corporate action on the part of Borrower and the other parties
delivering any of such documents, as the case may be. The organizational
documents of the Borrower, the REIT and the Guarantor Subsidiaries have not
been modified in any material respect since August 16, 1999.

NO CONFLICT. The execution and delivery by Borrower and the Guarantor
Subsidiaries of this Amendment and the performance by Borrower of the Credit
Agreement by Borrower do not and will not (i) violate any provision of any law
or any governmental rule or regulation applicable to Borrower or any of its
Subsidiaries, their respective Organization Documents or any order, judgment or
decree of any court or other agency of government binding on Borrower, the REIT
or any of their Subsidiaries, (ii) conflict with, result in a breach of or
constitute (with due notice or lapse of time or both) a default under any
Contractual Obligation of Borrower, the REIT or any of their Subsidiaries,
(iii) result in or require the creation or imposition of any Lien upon any of
the properties or assets of Borrower, the REIT or any of their Subsidiaries, or
(iv) require any approval of stockholders or any approval or consent of any
Person under any Contractual Obligation of Borrower, the REIT or any of their
Subsidiaries.

GOVERNMENTAL CONSENTS. The execution and delivery by Borrower and the Guarantor
Subsidiaries of this Amendment and the performance by Borrower and the
Guarantor Subsidiaries under the Credit Agreement do not and will not require
any registration with, consent or approval of, or notice to, or other action
to, with or by, any federal, state or other governmental authority or
regulatory body.

BINDING OBLIGATION. The Credit Agreement, as amended by this Amendment, has
been duly executed and delivered by Borrower and the Guarantor Subsidiaries, as
applicable, and is enforceable against Borrower and/or the Guarantor
Subsidiaries, as applicable, in accordance with its respective terms, except as
may be limited by bankruptcy, insolvency, reorganization, moratorium or similar
laws relating to or limiting creditors' rights generally or by equitable
principles relating to enforceability.

INCORPORATION OF REPRESENTATIONS AND WARRANTIES FROM CREDIT AGREEMENT. The
representations and warranties contained in Section 5 of the Credit Agreement
are and will be true, correct and complete in all material respects on and as
of the Amendment Effective Date to



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the same extent as though made on and as of such date, except representations
and warranties solely to the extent such representations and warranties
specifically relate to an earlier date, in which case they were true, correct
and complete in all material respects on and as of such earlier date.

ACKNOWLEDGEMENT AND CONSENT

                  Guarantor Subsidiaries are party to that certain Payment
Guaranty of REIT and of Preferred Stock Subsidiaries dated August 16, 1999 and
that certain Payment Guaranty of Non-Preferred Stock Subsidiaries dated August
16, 1999, in each case as amended by the Amended and Restated Credit Agreement
dated March 15, 2000 and as amended at even date herewith, pursuant to which
Guarantor Subsidiaries have guarantied the Obligations. Nothing in this Section
4 shall be construed to make the Guarantor Subsidiaries a party to the Credit
Agreement or to create any obligation in respect thereof except pursuant to
each Guaranty.

                  Each Guarantor Subsidiary hereby acknowledges that it has
reviewed the terms and provisions of the Credit Agreement and this Amendment
and consents to the amendment of the Credit Agreement effected pursuant to this
Amendment. Each Guarantor Subsidiary hereby confirms that each Guaranty to
which it is a party or otherwise bound will continue to guaranty or secure, as
the case may be, to the fullest extent possible the payment and performance of
all of the "Indebtedness" (as defined in the applicable Guaranty), including
without limitation the payment and performance of all such "Indebtedness," as
the case may be, with respect to the Obligations of Borrower now or hereafter
existing under or in respect of the Credit Agreement (as amended hereby) and
the Notes defined therein.

                  Each Guarantor Subsidiary acknowledges and agrees that any
Guaranty to which it is a party or otherwise bound shall continue in full force
and effect and that all of its obligations thereunder shall be valid and
enforceable and shall not be impaired or limited by the execution or
effectiveness of this Amendment. Each Guarantor Subsidiary represents and
warrants that all representations and warranties contained in the Credit
Agreement and the Guaranty to which it is a party or otherwise bound are true,
correct and complete in all material respects on and as of the Amendment
Effective Date to the same extent as though made on and as of that date, except
to the extent such representations and warranties specifically relate to an
earlier date, in which case they were true, correct and complete in all
material respects on and as of such earlier date.

                  Each Guarantor Subsidiary acknowledges and agrees that (i)
notwithstanding the conditions to effectiveness set forth in this Amendment,
such Guarantor Subsidiary is not required by the terms of the Credit Agreement
or any other Loan Document to consent to the amendments to the Credit Agreement
effected pursuant to this Amendment and (ii) nothing in the Credit Agreement,
this Amendment or any other Loan Document shall be deemed to require the
consent of such Guarantor Subsidiary to any future amendments to the Credit
Agreement.




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<PAGE>   6


MISCELLANEOUS

REFERENCE TO AND EFFECT ON THE CREDIT AGREEMENT AND THE OTHER LOAN DOCUMENTS.

On and after the Amendment Effective Date, each reference in the Credit
Agreement to "this Agreement", "hereunder", "hereof", "herein" or words of like
import referring to the Credit Agreement, and each reference in the other Loan
Documents to the "Credit Agreement", "thereunder", "thereof" or words of like
import referring to the Credit Agreement shall mean and be a reference to the
Credit Agreement, as amended by this Amendment.

Except as specifically amended by this Amendment, the Credit Agreement and the
other Loan Documents shall remain in full force and effect and are hereby
ratified and confirmed.

The execution, delivery and performance of this Amendment shall not, except as
expressly provided herein, constitute a waiver of any provision of, or operate
as a waiver of any right, power or remedy of Administrative Agent or any Lender
under, the Credit Agreement or any of the other Loan Documents.

FEES AND EXPENSES. Borrower acknowledges that all reasonable costs, fees and
expenses incurred by Administrative Agent and its counsel with respect to this
Amendment and the documents and transactions contemplated hereby shall be for
the account of Borrower.

HEADINGS. Section and subsection headings in this Amendment are included herein
for convenience of reference only and shall not constitute a part of this
Amendment for any other purpose or be given any substantive effect.

COUNTERPARTS; EFFECTIVENESS. This Amendment may be executed in any number of
counterparts and by different parties hereto in separate counterparts, each of
which when so executed and delivered shall be deemed an original, but all such
counterparts together shall constitute but one and the same instrument;
signature pages may be detached from multiple separate counterparts and
attached to a single counterpart so that all signature pages are physically
attached to the same document. This Amendment shall become effective upon the
execution of a counterpart hereof by Borrower and the Requisite Lenders, and
receipt by Borrower and Administrative Agent of written, facsimile or
telephonic notification of such execution and authorization of delivery
thereof.

                 [Signatures on Attached Pages S-1 through S-3]



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<PAGE>   7


                  IN WITNESS WHEREOF, the parties hereto have caused this
Amendment to be duly executed and delivered as of the day and year first
written above.

                             BORROWER

                             AIMCO PROPERTIES, L.P.,
                             a Delaware limited partnership

                             By:  AIMCO - GP, INC.,
                                  a Delaware corporation, its general partner


                             By:   /s/ PETER K. KOMPANIEZ
                                   --------------------------------------------
                                   Peter K. Kompaniez
                                   President


                             Notices to be sent to:

                             2000 South Colorado Boulevard
                             Tower 2, Suite 2-1000
                             Denver, Colorado 80222
                             Attention: Paul McAuliffe
                             Executive Vice President & Chief Financial Officer
                             Facsimile: (303) 691-4317



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                             BANK OF AMERICA

                             BANK OF AMERICA, N.A.,
                             as Administrative Agent


                             By:    /s/ ROBERT N. ALLEN
                                    -------------------------------------------
                             Name:  Robert N. Allen
                             Title: Vice President


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<PAGE>   9


                             U.S. BANK NATIONAL ASSOCIATION


                             U.S. BANK NATIONAL ASSOCIATION,
                             as a Lender


                             By:   /s/ CYD D. PETRE
                                  ---------------------------------------------
                                  Name:  Cyd D. Petre
                                  Title: Vice President




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<PAGE>   10




The undersigned Guarantor Subsidiaries hereby execute this Amendment solely for
the purposes of acknowledging the same and consenting thereto in accordance
with Section 4 thereof.


REIT AND PREFERRED STOCK SUBSIDIARIES:

APARTMENT INVESTMENT AND
MANAGEMENT COMPANY


By: /s/ PETER K. KOMPANIEZ
    -------------------------------
    Peter K. Kompaniez
    President


AIMCO/NHP HOLDINGS, INC.


By: /s/ PETER K. KOMPANIEZ
    -------------------------------
    Peter K. Kompaniez
    President


NHP A&R SERVICES, INC.


By: /s/ PETER K. KOMPANIEZ
    -------------------------------
    Peter K. Kompaniez
    President


NHP MANAGEMENT COMPANY


By: /s/ THOMAS TOOMEY
    ------------------------------
    Thomas Toomey
    President




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NON-PREFERRED STOCK SUBSIDIARIES


         AIMCO Anchorage, L.P.
         AIMCO Bay Club, L.P.
         AIMCO Bridgewater, L.P.
         AIMCO Copperfield, L.P.
         AIMCO Crows Nest, L.P.
         AIMCO Group, L.P.
         AIMCO Hampton Hill, L.P.
         AIMCO Hastings Place, L.P.
         AIMCO LT, L.P.
         AIMCO Oak Falls, L.P.
         AIMCO Park at Cedar Lawn, L.P.
         AIMCO Peppermill Place, L.P.
         AIMCO Recovery Fund, L.P.
         AIMCO Seaside Point, L.P.
         AIMCO Signature Point, L.P.
         AIMCO Stirling Court, L.P.
         AIMCO Sunbury, L.P.
         AIMCO Township at Highlands, L.P.
         AIMCO UT, L.P.
         AIMCO West Trails, L.P.

         By:      AIMCO Holdings, L.P., as their general partner

                  By:      AIMCO Holdings QRS, Inc., its
                           general partner

                           By:   /s/ PETER K. KOMPANIEZ
                                 ----------------------
                                 Peter K. Kompaniez
                                 President


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         AIMCO Bay Club II, L.P.

         By:      AIMCO Bay Club, L.P., its general partner

                  By:      AIMCO Holdings, L.P., as their general partner

                           By:      AIMCO Holdings QRS, Inc., its
                                    general partner

                                    By:     /s/ PETER K. KOMPANIEZ
                                            ----------------------
                                            Peter K. Kompaniez
                                            President


         AIMCO Holdings, L.P.

         By:      AIMCO Holdings QRS, Inc., its
                  general partner

                           By:      /s/ PETER K. KOMPANIEZ
                                    ----------------------
                                    Peter K. Kompaniez
                                    President


         Ambassador CRM Florida Partners, L.P.

         By:      Ambassador Florida Partners Limited Partnership, as its
                  general partner

                  By:      Ambassador Florida Partners, Inc., as its
                           general partner

                           By:      /s/ PETER K. KOMPANIEZ
                                    ----------------------
                                    Peter K. Kompaniez
                                    President


                                       12

<PAGE>   13

         Ambassador I, L.P.

         By:      Ambassador I, Inc., its general partner

                  By:      /s/ PETER K. KOMPANIEZ
                           ----------------------
                           Peter K. Kompaniez
                           President


         Ambassador II, L.P.

         By:      Ambassador II, Inc., its general partner

                  By:      /s/ PETER K. KOMPANIEZ
                           ----------------------
                           Peter K. Kompaniez
                           President


         Ambassador VIII, L.P.

         By:      Ambassador VIII, Inc., its general partner

                  By:      /s/ PETER K. KOMPANIEZ
                           ----------------------
                           Peter K. Kompaniez
                           President


         Ambassador IX, L.P.

         By:      Ambassador IX, Inc., its general partner

                  By:      /s/ PETER K. KOMPANIEZ
                           ----------------------
                           Peter K. Kompaniez
                           President




                                       13
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         Ambassador Apartments, L.P.
         Property Asset Management Services, L.P.

         By:      AIMCO Properties, L.P., as their general partner

                  By:      AIMCO-GP, Inc., its general partner

                           By:      /s/ PETER K. KOMPANIEZ
                                    ----------------------
                                    Peter K. Kompaniez
                                    President


         Ambassador X, L.P.

         By:      Ambassador X, Inc., its general partner

                  By:      /s/ PETER K. KOMPANIEZ
                           ----------------------
                           Peter K. Kompaniez
                           President


         Williamsburg L.P.

         By:      Ambassador IX, L.P.., its general partner

                  By:      Ambassador IX, Inc., its general partner

                           By:      /s/ PETER K. KOMPANIEZ
                                    ----------------------
                                    Peter K. Kompaniez
                                    President




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         Property Asset Management Services-California, LLC

         By:      Property Asset Management Services, L.P., its managing
                  general partner

                  By:      AIMCO Properties, L.P., its general partner

                           By:      AIMCO-GP, Inc., its general partner

                                    By:     /s/ PETER K. KOMPANIEZ
                                            ----------------------
                                            Peter K. Kompaniez
                                            President


         NHP Congress Management L.P.

                  By:      NHP-HG Six, Inc., its general partner

                           By:      /s/ PETER K. KOMPANIEZ
                                    ----------------------
                                    Peter K. Kompaniez
                                    President

         NPI-AP Management, L.P.

         By:      NPI Property Management Corporation, its
                  general partner

                  By:      /s/ PETER K. KOMPANIEZ
                           ----------------------
                           Peter K. Kompaniez
                           President





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<PAGE>   16




         AIMCO Residential Group, L.P.

         By:      AG Management, L.L.C., its general partner

                  By:      NHP Management Company, its
                           managing member

                           By:      /s/ THOMAS TOOMEY
                                    -----------------
                                    Thomas Toomey
                                    President


         Insignia Properties, L.P.

         By:      AIMCO/IPT, Inc., its general partner

                  By:      /s/ PETER K. KOMPANIEZ
                           ----------------------
                           Peter K. Kompaniez
                           President

         AIMCO Calhoun, Inc.
         AIMCO Holdings QRS, Inc.
         AIMCO LJ Tucson, Inc.
         AIMCO Properties Finance Corp.
         AIMCO Somerset, Inc.
         AIMCO/Brant Rock, Inc.
         AIMCO/Beacon Hill, Inc.
         AIMCO/Blossomtree, Inc.
         AIMCO/Colonnade, Inc.
         AIMCO/Foothills, Inc.
         AIMCO/Foxbay, Inc.
         AIMCO/Foxtree, Inc.
         AIMCO/Freedom Place, Inc.
         AIMCO/Grovetree, Inc.
         AIMCO/Hazeltree, Inc.
         AIMCO/Hiddentree, Inc.
         AIMCO/IPT, Inc.
         AIMCO/Islandtree, Inc.
         AIMCO/Olmos, Inc.
         AIMCO/Orchidtree, Inc.
         AIMCO/OTC QRS, Inc.
         AIMCO/Pine Creek, Inc.
         AIMCO/Polo Park, Inc.



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<PAGE>   17



         AIMCO/Quailtree, Inc.
         AIMCO/Rivercrest, Inc.
         AIMCO/Sand Castles, Inc.
         AIMCO/Sand Pebble, Inc.
         AIMCO/Shadetree, Inc.
         AIMCO/Shadow Lake, Inc.
         AIMCO/Silktree, Inc.
         AIMCO/Surrey Oaks, Inc.
         AIMCO/Tall Timbers, Inc.
         AIMCO/The Hills, Inc.
         AIMCO/Timbertree, Inc.
         AIMCO/Twinbridge, Inc.
         AIMCO/Wickertree, Inc.
         AIMCO/Wildflower, Inc.
         AIMCO/Windsor Landing, Inc.
         AIMCO/Woodhollow, Inc.
         AIMCO/Wydewood, Inc.
         AIMCO/Yorktree, Inc.
         AIMCO-LP, Inc.
         AIMCO-GP, Inc.
         Ambassador I, Inc.
         Ambassador II, Inc.
         Ambassador IV, Inc.
         Ambassador V, Inc.
         Ambassador VIII, Inc.
         Ambassador Texas, Inc.
         Ambassador X, Inc.
         Ambassador XI, Inc.
         Ambassador Florida Partners Inc.
         Angeles Realty Corporation II
         NHP Multi-Family Capital Corporation
         NHP Real Estate Corporation
         A.J. Two, Inc.
         AIMCO Equity Services, Inc.
         NHP Texas Management Company
         NHP Puerto Rico Management Company
         NHP Florida Management Company
         NHP Maintenance Services Company
         NHP-HDV Ten, Inc.
         NHP-HDV Fourteen, Inc.
         NHP-HDV Sixteen, Inc.
         NHP-HDV 20, Inc.
         NHP-HS Two, Inc.




                                       17
<PAGE>   18







         Broadstreet Management, Inc.
         Rescorp Realty, Inc.
         Preferred Home Health, Inc.
         Security Management, Inc.
         Insignia Residential Group of Alabama, Inc.
         Insignia Residential Group of California, Inc.
         Insignia Residential Group of Texas, Inc.
         DBL Properties Corporation
         Colony of Springdale Properties, Inc.
         SF General, Inc.
         CPF XIV/St. Charleston, Inc.
         CPF XIV/Torrey Pines, Inc.
         CPF XIV/Sun River, Inc.
         CPF XIV/Lakeside Place, Inc.
         ConCap CCP/IV Stratford Place Properties, Inc.
         ConCap CCP/IV River's Edge Properties, Inc.
         ConCap Equities, Inc.
         ConCap Holdings, Inc.
         PRA, Inc.
         National Property Investors, Inc.

                  By:      /s/ PETER K. KOMPANIEZ
                           ----------------------
                           Peter K. Kompaniez
                           President



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<PAGE>   19



         Address Where Notices are to be Sent:

            To Guarantor:                   2000 South Colorado Boulevard
                                            Tower 2, Suite 2-1000
                                            Denver, Colorado 80222

            To Administrative Agent:        BANK OF AMERICA, N.A.
                                            CA9-706-06-02
                                            555 South Flower Street, 6th Floor
                                            Los Angeles, California 90071
                                            Attention: Manager - Unit #1313

            To Lenders:                     Per the Credit Agreement




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