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Exhibit 10.6
 UNCONDITIONAL GUARANTY OF PAYMENT AND PERFORMANCE
  (a)
    
    the full and prompt payment when due, whether by acceleration or otherwise,
either before or after maturity thereof, in accordance with the terms of the Credit
Agreement, of those outstanding Notes made by Borrower to the order of each Lender in
the aggregate principal amount equal to the then outstanding aggregate principal
amount of the Loans (which amount shall not exceed the Maximum Loan Amount in the
aggregate) together with interest as provided in the Credit Agreement, together with
any renewals, modifications, consolidations, restatements and extensions thereof; and(b)
    
    the full and prompt payment and performance of all of the other Borrower
Obligations of Borrower to Agent and the Lenders under the terms of the Credit
Agreement, the Environmental Indemnity, the Pledge Agreement and each other Credit
Document to which Borrower is a party.
 1.
    
    Agreement to Pay and Perform; Costs of Collection. Guarantor does hereby agree that
if any Note is not paid by Borrower in accordance with its terms, or if any and all sums which
are now or may hereafter become due from Borrower to Agent and/or the Lenders under the Credit
Documents are not paid by Borrower in accordance with their terms, or if any and all other
Borrower Obligations are not performed by Borrower in accordance with their terms, Guarantor
will immediately make such payments and perform such Borrower Obligations. Guarantor further
agrees to pay Agent and/or the Lenders on demand all costs and expenses (including court costs
and reasonable attorneys fees and disbursements) paid or incurred by Agent and/or the Lenders
in endeavoring to collect the Borrower Obligations, to enforce any of the Borrower
Obligations, or any portion thereof, or to enforce this Guaranty, and until paid to Agent
and/or the Lenders,
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such sums shall bear interest at the Default Rate unless collection from Guarantor of
interest at such rate would be contrary to applicable law, in which event such sums shall
bear interest at the highest rate which may be collected from Guarantor under applicable
law. Any payment or other performance of the Borrower Obligations by Guarantor under this
Guaranty shall result in, (i) with respect to any payments made, a corresponding reduction
in the amount of Borrower Obligations, and (ii) with respect to any performance other than
payments made, Borrower being deemed to have fulfilled such performance.
 2.
    
    Rights of Agent and/or the Lenders to Deal with Collateral, Borrower and Other
Persons. Guarantor hereby consents and agrees that Agent and/or the Lenders may at any
time, and from time to time, without thereby releasing Guarantor from any liability hereunder
and without notice to or further consent from Guarantor, either with or without consideration:
(i) release or surrender any Collateral, lien or other security of any kind or nature
whatsoever held by it or by any Person on its behalf or for its account, securing any of the
Borrower Obligations; (ii) substitute for any Collateral so held by it, other collateral of
any kind; (iii) modify the terms of any Credit Document except to the extent the consent of
Borrower is required to make any such modifications; (iv) extend or renew the Note for any
period except to the extent the consent of Borrower is required to make any such
modifications; (v) grant releases, compromises and indulgences with respect to any Credit
Document and to any Persons now or hereafter liable thereunder or hereunder; (vi) release any
other guarantor, surety, endorser or accommodation party of any Credit Document; or (vii) take
or fail to take any action of any type whatsoever under this Guaranty or any Credit Document.
No such action which Agent and/or the Lenders shall take or fail to take in connection with
any Credit Document, or any Collateral securing the payment of the Borrower Obligations to
Agent and/or the Lenders or for the performance of any of the Borrower Obligations or other
undertakings of Borrower, nor any course of dealing with Borrower or any other Person, shall
release Guarantors obligations hereunder, affect this Guaranty in any way or afford Guarantor
any recourse against Agent and/or the Lenders. The provisions of this Guaranty shall extend
and be applicable to all renewals, amendments, extensions, consolidations, restatements and
modifications of any Credit Document, and any and all references herein to any Credit Document
shall be deemed to include any such renewals, extensions, amendments, consolidations,
restatements or modifications thereof.
 3.
    
    No Contest with Agent/Lender; Subordination. So long as any Borrower Obligation
remains unpaid or undischarged, Guarantor will not, by paying any sum recoverable hereunder
(whether or not demanded by Agent and/or the Lenders) or by any means or on any other ground,
claim any set-off or counterclaim against Borrower in respect of any liability of Borrower to
Guarantor or, in proceedings under federal bankruptcy law or insolvency proceedings of any
nature, prove in competition with Agent and/or the Lenders in respect of any payment hereunder
or be entitled to have the benefit of any counterclaim or proof
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of claim or dividend or payment by or on behalf of Borrower or the benefit of any other
security for any Borrower Obligation which, now or hereafter, Agent and/or the Lenders may
hold or in which it may have any share. Guarantor hereby subordinates any and all
indebtedness of Borrower now or hereafter owed to Guarantor to all of the Borrower
Obligations, and agrees with Agent and/or the Lenders that during the existence of an Event
of Default (a) Guarantor shall not demand or accept any payment from Borrower on account of
such indebtedness, (b) Guarantor shall not claim any offset or other reduction of
Guarantors obligations hereunder because of any such indebtedness, and (c) Guarantor shall
not take any action to obtain any interest in any of the Collateral because of any such
indebtedness.
 4.
    
    Waiver of Defenses. Guarantor hereby agrees that its obligations hereunder shall not
be affected or impaired by, and hereby waives and agrees not to assert or take advantage of
any defense based on:
 (a)
    
    any statute of limitations in any action hereunder or for the collection,
payment or performance of any of the Borrower Obligations;(b)
    
    the incapacity or lack of authority of Borrower or any other Person, the
death or disability of Borrower or Guarantor or any other Person, or the failure of
Agent and/or the Lenders to file or enforce a claim against the estate (either in
administration, bankruptcy or in any other proceeding) of Borrower or Guarantor or any
other Person;(c)
    
    the dissolution or termination of existence of Borrower;(d)
    
    the voluntary or involuntary liquidation, sale or other disposition of all or
substantially all of the assets of Borrower;(e)
    
    the voluntary or involuntary receivership, insolvency, bankruptcy, assignment
for the benefit of creditors, reorganization, assignment, composition, or readjustment
of, or any similar proceeding affecting, Borrower or Guarantor, or any of Borrowers
or Guarantors properties or assets;(f)
    
    the failure of Agent and/or the Lenders to give notice of the existence,
creation or incurrence of any new or additional Borrower Obligations or of any action
or nonaction on the part of any other Person whomsoever in connection with any
obligation hereby guaranteed;(g)
    
    any failure or delay of Agent and/or the Lenders to commence an action
against Borrower, to assert or enforce any remedies against Borrower under any Credit
Document, or to realize upon any Collateral or other security.
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(h)
    
    any failure of any duty on the part of Agent and/or the Lenders to disclose
to Guarantor any facts it may now or hereafter know regarding Borrower, whether such
facts materially increase the risk to Guarantor or not;(i)
    
    failure to accept or give notice of acceptance of this Guaranty by Agent
and/or the Lenders;(j)
    
    failure to make or give notice of presentment and demand for payment or
performance of any of the Borrower Obligations;(k)
    
    failure to make or give protest and notice of dishonor or of default to
Guarantor or to any other party to any of the Credit Documents with respect to any of
the Borrower Obligations;(l)
    
    failure to give any and all other notices whatsoever to which Guarantor might
otherwise be entitled other than notice of a claim being brought under this Guaranty;(m)
    
    any lack of diligence by Agent and/or the Lenders in collection, protection
or realization upon any Collateral securing the payment or performance of the Borrower
Obligations;(n)
    
    the invalidity or unenforceability of any Note, the Credit Agreement or any
other Credit Document;(o)
    
    the compromise, settlement, release or termination of any or all of the
Borrower Obligations with respect to any portion of the Borrower Obligations not
satisfied pursuant to such compromise, settlement, release or termination;(p)
    
    any transfer by Borrower of all or any part of the Collateral securing the
Borrower Obligations;(q)
    
    the failure of Agent and/or the Lenders to perfect any security or to extend
or renew the perfection of any security; or(r)
    
    to the fullest extent permitted by law, any other legal, equitable or surety
defenses whatsoever to which Guarantor might otherwise be entitled, it being the
intention that the obligations of Guarantor hereunder are absolute, unconditional and
irrevocable.
 5.
    
    Guaranty of Payment and Performance and Not of Collection. This is a Guaranty of
payment and performance and not of collection. The liability of Guarantor under this Guaranty
shall be primary, direct and immediate and not conditional or
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contingent upon the pursuit of any remedies against Borrower or any other Person, nor
against Collateral or other securities or liens available to Agent and/or the Lenders, its
successors, successors in title, endorsees or assigns. Guarantor hereby waives any right
to require that an action be brought against Borrower or any other Person or to require
that resort be had to the Collateral, any other security or to any balance of any deposit
account or credit on the books of Agent and/or the Lenders in favor of Borrower or any
other Person.
 6.
    
    Rights and Remedies of Agent/Lender. Upon the occurrence of an Event of Default,
Agent shall have the right to enforce its rights, powers and remedies under the Credit
Agreement, any other Credit Documents, hereunder or under any other agreement, document or
instrument now or hereafter evidencing, securing or otherwise relating to the Borrower
Obligations, in any order, and all rights, powers and remedies available to Agent in such
event shall be nonexclusive and cumulative of all other rights, powers and remedies provided
thereunder or hereunder or by law or in equity. Accordingly, Guarantor hereby authorizes and
empowers Agent upon the occurrence of any Event of Default, at its sole discretion, and
without notice to Guarantor, to exercise any right or remedy which Agent may have, as to any
Collateral, whether real, personal or intangible. At any public or private sale of any
Collateral for any of the Borrower Obligations, Agent may, in its discretion, purchase all or
any part of such Collateral so sold or offered for sale for its own account and may apply
against the amount bid therefor all or any part of the balance due it pursuant to the terms of
the Credit Agreement, the Notes, or any other Credit Document without prejudice to Agents
remedies hereunder against Guarantor for deficiencies. If the Borrower Obligations are
partially paid by reason of the election of Agent to pursue any of the remedies available to
Agent, or if such Borrower Obligations are otherwise partially paid, this Guaranty shall
nevertheless remain in full force and effect, and Guarantor shall remain liable for the entire
remaining balance of the Borrower Obligations even though any rights which Guarantor may have
against Borrower may be destroyed or diminished by the exercise of any such remedy.
 7.
    
    Application of Payments. Guarantor hereby authorizes Agent and/or the Lenders,
without notice to Guarantor, to apply all payments and credits received from Borrower or from
Guarantor or realized from any Collateral or other security in the manner set forth in
applicable provisions of the Credit Agreement or any other Credit Document, and for purposes
of such provisions, the Guarantors obligations hereunder shall be considered part of the
Borrower Obligations.
 8.
    
    Business Failure, Bankruptcy or Insolvency. In the event of the business failure of
Guarantor or if there shall be pending any bankruptcy or insolvency case or proceeding with
respect to Guarantor under federal bankruptcy law or any other applicable law or in connection
with the insolvency of Guarantor, or if a liquidator, receiver, or trustee shall have been
appointed for Guarantor or Guarantors properties or assets, Agent may file such proofs of
claim and other
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papers or documents as may be necessary or advisable in order to have the claims of Lenders
allowed in any proceedings relative to Guarantor, or any of Guarantors properties or
assets, and, irrespective of whether the Borrower Obligations shall then be due and
payable, by declaration or otherwise, Agent shall be entitled and empowered to file and
prove a claim for the whole amount of any sums or sums owing with respect to the Borrower
Obligations, and to collect and receive any moneys or other property payable or deliverable
on any such claim.
 9.
    
    Changes in Writing; No Revocation. This Guaranty may not be changed orally, and no
obligation of Guarantor can be released or waived by Agent except by a writing signed by a
duly authorized officer of Agent. This Guaranty shall be irrevocable by Guarantor until all
of the Borrower Obligations have been completely repaid and performed.
 Notices
 
 
 11.
    
    Governing Law. Guarantor acknowledges and agrees that this Guaranty and the
obligations of Guarantor hereunder shall be governed by and interpreted and determined in
accordance with the laws of The Commonwealth of Massachusetts (excluding the laws applicable
to conflicts or choice of law).
 12.
    
    CONSENT TO JURISDICTION; WAIVERS. GUARANTOR HEREBY IRREVOCABLY AND UNCONDITIONALLY
(A) SUBMITS TO PERSONAL JURISDICTION IN THE COMMONWEALTH OF MASSACHUSETTS OVER ANY SUIT,
ACTION OR PROCEEDING ARISING OUT OF OR RELATING TO THIS GUARANTY, AND (B) WAIVES ANY AND ALL
PERSONAL RIGHTS UNDER THE LAWS OF ANY STATE (I) TO THE RIGHT, IF ANY, TO TRIAL BY JURY, (II)
TO OBJECT TO JURISDICTION WITHIN THE COMMONWEALTH OF MASSACHUSETTS OR VENUE IN ANY
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PARTICULAR FORUM WITHIN THE COMMONWEALTH OF MASSACHUSETTS, AND (III) TO THE RIGHT, IF ANY,
TO CLAIM OR RECOVER ANY SPECIAL, EXEMPLARY, PUNITIVE OR CONSEQUENTIAL DAMAGES OR ANY
DAMAGES OTHER THAN ACTUAL DAMAGES. GUARANTOR AGREES THAT, IN ADDITION TO ANY METHODS OF
SERVICE OF PROCESS PROVIDED FOR UNDER APPLICABLE LAW, ALL SERVICE OF PROCESS IN ANY SUCH
SUIT, ACTION OR PROCEEDING MAY BE MADE BY CERTIFIED OR REGISTERED MAIL, RETURN RECEIPT
REQUESTED, DIRECTED TO GUARANTOR AT THE ADDRESS SET FORTH IN PARAGRAPHS 10 AND 16(c)
HEREIN, AND SERVICE SO MADE SHALL BE COMPLETE FIVE (5) DAYS AFTER THE SAME SHALL BE SO
MAILED. NOTHING CONTAINED HEREIN, HOWEVER, SHALL PREVENT LENDER FROM BRINGING ANY SUIT,
ACTION OR PROCEEDING OR EXERCISING ANY RIGHTS AGAINST ANY SECURITY AND AGAINST GUARANTOR
PERSONALLY, AND AGAINST ANY PROPERTY OF GUARANTOR, WITHIN ANY OTHER STATE. INITIATING SUCH
SUIT, ACTION OR PROCEEDING OR TAKING SUCH ACTION IN ANY STATE SHALL IN NO EVENT CONSTITUTE
A WAIVER OF THE AGREEMENT CONTAINED HEREIN THAT THE LAWS OF THE COMMONWEALTH OF
MASSACHUSETTS SHALL GOVERN THE RIGHTS AND OBLIGATIONS OF GUARANTOR AND LENDER HEREUNDER OR
OF THE SUBMISSION HEREIN MADE BY GUARANTOR TO PERSONAL JURISDICTION WITHIN THE COMMONWEALTH
OF MASSACHUSETTS.
 13.
    
    Successors and Assigns. The provisions of this Guaranty shall be binding upon
Guarantor and its heirs, successors, successors in title, legal representatives, and assigns,
and shall inure to the benefit of Agent, the Lenders, its successors, successors in title,
legal representatives and assigns.
 14.
    
    Assignment by Lender. This Guaranty is assignable by the Agent and the Lenders in
whole or in part in conjunction with any assignment of any Note or portions thereof, and any
assignment hereof or any transfer or assignment of any Note or portions thereof by the Lenders
shall operate to vest in any such assignee the rights and powers, in whole or in part, as
appropriate, herein conferred upon and granted to Agent and the Lenders.
 15.
    
    Severability. If any term or provision of this Guaranty shall be determined to be
illegal or unenforceable, all other terms and provisions hereof shall nevertheless remain
effective and shall be enforced to the fullest extent permitted by law.
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16.
    
    Miscellaneous.
 (a)
    
    The guaranteed Obligations are intended to be used solely for commercial or
business purposes and not for any personal, family or household purpose.(b)
    
    The Guarantor agrees that any impairment of the Guarantors rights of
subrogation or reimbursement shall not affect the Guarantors obligations under this
Guaranty.(c)
    
    The Guarantors address is 2800 Post Oak Boulevard, Suite 5000, Houston,
Texas 77056-6118, and such address may be used by the Agent and the Lenders in any
action against the Guarantor.
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HINES REAL ESTATE INVESTMENT TRUST, INC., a
Maryland corporationBy:
/s/ Frank R. ApolloName: Frank R. ApolloTitle: Chief Accounting Officer