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                                                                   EXHIBIT 10.33

                       SIXTH AMENDMENT TO CONTRACT OF SALE

        This SIXTH AMENDMENT TO CONTRACT OF SALE (this "Amendment") is made and
entered into effective as of the ____ day of June, 2004 (the "Effective Date"),
by and among VORTISCH HOLDINGS, L.P., a Texas limited partnership ("Seller"),
CANTEX REALTIES, INC., a Texas corporation ("Cantex"), REALTY AMERICA GROUP
(4245 CENTRAL), LP, a Texas limited partnership ("Original Purchaser"), and
BEHRINGER HARVARD SHORT-TERM OPPORTUNITY FUND I LP, a Texas limited partnership
("Purchaser").

                             PRELIMINARY STATEMENTS:

        The following preliminary statements are a material part of this
Amendment:

        A.      Seller, Cantex and Realty America Group I, LP, as predecessor in
interest to Original Purchaser made and entered into that certain Contract of
Sale, dated effective April 16, 2004 (the "Original Contract"), with respect to
certain real property located on that certain tract or parcel of land situated
in the City of Dallas, Dallas County, Texas, which is more particularly
described in the Contract (the "Property"); as amended by that certain First
Amendment to Contract of Sale (the "First Amendment"); as amended by that
certain Second Amendment to Contract of Sale (the "Second Amendment"); as
amended by that certain Third Amendment to Contract of Sale (the "Third
Amendment"); as amended by that certain Fourth Amendment to Contract of Sale
(the "Fourth Amendment"); as amended by that certain Fifth Amendment to Contract
of Sale (the "Fifth Amendment") (the Contract, the First Amendment, the Second
Amendment, the Third Amendment, the Fourth Amendment and the Fifth Amendment are
hereinafter collectively referred to as the "Contract").

        B.      Cantex is only a party to this Amendment and the Contract as is
necessary for Original Purchaser and Purchaser to enforce certain
representations and warranties provided by Cantex to Purchaser under the
Contract.

        C.      Seller, Cantex, and Original Purchaser, and Purchaser desire to
amend the Contract as set forth below.

                                   AGREEMENTS:

        NOW THEREFORE, in consideration of the agreements to sell and purchase
the Property and the mutual covenants and agreements contained in this Amendment
and in the Contract, and other good and valuable consideration, the receipt and
adequacy of which are hereby acknowledged, Seller, and Purchaser hereby agree as
follows:

1.      ASSIGNMENT. Seller hereby consents to, ratifies and accepts the
assignment of the Contract, and all rights, duties and obligations under the
Contract, from Realty America Group (4245 Central), LP to Behringer Harvard
Short-Term Opportunity Fund I LP. Original Purchaser shall be forever released
of its obligations under the Contract upon the Effective Date of this

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Amendment. Any reference in the Contract to Purchaser shall, from the Effective
Date of this Amendment, refer to Behringer Harvard Short-Term Opportunity Fund I
LP.

2.      CLOSING EXTENSION. Pursuant to the terms of the Fifth Amendment, the
Closing of the Contract was to occur on or before Friday, July 30, 2004. Upon
payment of the Closing Extension Deposit (defined below), the parties hereby
agree to extend the Closing Date to on or before Monday, August 16, 2004.

3.      CLOSING DEPOSIT. As consideration for the extension of the Closing Date,
Purchaser hereby agrees that if, as and when this Amendment is fully executed,
Purchaser shall, within three (3) business days following the Effective Date of
this Amendment deposit an additional One Hundred Thousand and No/100s Dollars
($100,000.00) (the "Closing Extension Deposit") with the Title Company. The
Closing Extension Deposit shall replace the Earnest Money deposit totaling One
Hundred Thousand and No/100s Dollars ($100,000.00), and shall be refundable
pursuant to the terms of the Contract. Upon the funding of the Closing Extension
Deposit, the Title Company is hereby instructed to release the original Earnest
Money deposit to Seller.

4.      CAPITALIZED TERMS. Capitalized terms used but not defined in this
Amendment shall have the same meaning as those in the Contract, unless otherwise
noted herein.

5.      RATIFICATION OF CONTRACT. Except as specifically modified by this
Amendment, all of the other terms and provisions of the Contract shall remain in
full force and effect, and are hereby ratified and confirmed by Seller, Cantex,
Original Purchaser and Purchaser. Notwithstanding the foregoing, in the event
there is any conflict between the terms and provisions of the Contract and this
Amendment, the terms and provisions of this Amendment shall control.

6.      REPRESENTATIONS AND WARRANTIES. Seller, Cantex, Original Purchaser, and
Purchaser represent and warrant to each other respectively that they have the
requisite power and authority to enter into this Amendment; that all necessary
and appropriate approvals, authorizations and other steps have been taken to
effect the legality of this Amendment; that the signatories executing this
Amendment are authorized to do so on behalf of Seller, Cantex, Original
Purchaser and Purchaser; and that this Amendment is valid and binding upon and
enforceable against Seller, Cantex, Original Purchaser and Purchaser.

7.      COUNTERPARTS. This Amendment may be executed in any number of
counterparts, each of which shall be deemed an original. Facsimile copies of the
signature pages to this Amendment shall be deemed to be originals for all
purposes of this Amendment.

8.      FINAL AGREEMENT. This Amendment and the Contract cover in full, each and
every final agreement of every kind or nature whatsoever between Seller, Cantex,
Original Purchaser and Purchaser concerning the Property, and all preliminary
negotiations and agreements whatsoever of every kind or nature are merged into
this Amendment and the Contract. This Amendment and the Contract cannot be
changed or modified in any manner other than by written amendment or
modification executed by Seller, Cantex and Purchaser.


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9.      SUCCESSORS AND ASSIGNS. This Amendment is binding upon and inures to the
benefit of Seller, Cantex, Original Purchaser and Purchaser and their respective
successors and assigns.

        IN WITNESS WHEREOF, Seller, Cantex, Original Purchaser and Purchaser
have caused this Amendment to be duly executed as of the Effective Date.

                                SELLER:

                                VORTISCH HOLDINGS, L.P.,
                                a Texas limited partnership

                                By: VORTISCH INVESTMENTS, INC.,
                                    a Delaware corporation
                                    its general partner

                                    By:
                                             -----------------------------------
                                             Hermann Vortisch
                                             President

                                    Date of Signature: July ____, 2004

                                PURCHASER:

                                BEHRINGER HARVARD SHORT-TERM OPPORTUNITY FUND I
                                LP, a Texas limited partnership

                                By: BEHRINGER HARVARD 4245 CENTRAL GP, LLC,
                                    a Texas limited liability company
                                    its general partner

                                    By:
                                             -----------------------------------
                                             Gerald J. Reihsen, III
                                             Member

                                    Date of Signature: July  ____, 2004

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                                ORIGINAL PURCHASER:

                                REALTY AMERICA GROUP (4245 CENTRAL), LP,
                                a Texas limited partnership

                                By: REALTY AMERICA GROUP INVESTMENTS, LLC,
                                    a Texas limited liability company
                                    its general partner

                                    By:
                                             -----------------------------------
                                             Webb M. Sowden, III
                                             Member

                                Date of Signature: July  ____, 2004

                                CANTEX:

                                CANTEX REALTIES, INC.,
                                a Texas corporation


                                By:
                                      ------------------------------------------
                                Name:
                                      ------------------------------------------
                                Its:
                                      ------------------------------------------

                                Date of Signature: July  ____, 2004