GUARANTY OF NON-RECOURSE AND ENVIRONMENTAL INDEMNITY OBLIGATIONS

EXHIBIT 10.6

GUARANTY OF NON-RECOURSE AND

ENVIRONMENTAL INDEMNITY OBLIGATIONS

THIS GUARANTY OF NON-RECOURSE AND ENVIRONMENTAL INDEMNITY OBLIGATIONS (" Guaranty "), dated as of March 18, 2008, is made by PRIME GROUP REALTY, L.P. , a Delaware limited partnership (the " Guarantor "), in favor of (i)  GENERAL ELECTRIC CAPITAL CORPORATION , a Delaware corporation (" GECC "), as Collateral Agent for the Note A Lenders and the Note B Lenders (in such capacity, " Collateral Agent "), (ii)  ING USA ANNUITY AND LIFE INSURANCE COMPANY , an Iowa corporation (" ING "), and any subsequent holders from time to time (together with ING, collectively, the " Note   A Lenders ") of interests in that certain Promissory Note A dated the date of this Guaranty made by 330 N. WABASH AVENUE, L.L.C. , a Delaware limited liability company (the " Borrower "), and payable to the order of the ING in the original principal amount of $88,000,000 (such Promissory Note A, together with all promissory notes delivered in substitution or exchange thereof, in each case as the same may be from time to time consolidated, split, amended, modified, extended, renewed, substituted and/or supplemented, shall be collectively referred to in this Guaranty as " Note   A "), the provisions of which Note A are incorporated in this Guaranty by reference, and (iii) GECC and any subsequent holders from time to time (together with GECC, collectively, the " Note   B Lenders ") of interests in that certain Promissory Note B dated the date of this Guaranty made by the Borrower and payable to the order of GECC in the original principal amount of $100,000,000 (such Promissory Note B, together with all promissory notes delivered in substitution or exchange thereof, in each case as the same may be from time to time consolidated, split, amended, modified, extended, renewed, substituted and/or supplemented, shall be collectively referred to in this Guaranty as the " Note   B "), the provisions of which Note B are incorporated in this Guaranty by reference, and which Note B is executed pursuant to that certain Loan Agreement (Loan B) dated as of the date of this Guaranty among the Borrower, the Note B Lenders from time to time party thereto, and Collateral Agent (such Loan Agreement, as it may from time to time be supplemented, modified and amended, being referred to in this Guaranty as the " Agreement "). The Note A Lenders and the Note B Lenders are hereinafter sometimes collectively referred to as the " Lenders "). Capitalized terms used in this Guaranty and not otherwise defined are used with the meanings set forth in Note B.

Subject to the terms and conditions set forth in Note A, the Agreement, Note B and the Mortgages (as hereinafter defined), the Note A Lenders have agreed to make a loan to the Borrower in the aggregate principal amount of $88,000,000 (collectively, " Loan   A ") and the Note B Lenders have agreed to make loans to the Borrower in the aggregate amount of up to $100,000,000 (collectively, " Loan   B ") to provide financing for the Project (as defined in the

Agreement). Loan A and Loan B (collectively, the " Loans ") will be secured by (i) that certain Mortgage, Assignment of Leases, Security Agreement and Fixture Filing and (ii) that certain Leasehold Mortgage, Assignment of Leases, Security Agreement and Fixture Filing (collectively, the " Mortgages "), each executed by the Borrower in favor of Collateral Agent (on behalf of the Note A Lenders and the Note B Lenders) with respect to the Project. As a condition of the obligation of the Note A Lenders to make Loan A and the Note B Lenders to make Loan B, the Guarantor is required to execute and deliver to Collateral Agent, the Note A Lenders and the Note B Lenders this Guaranty.

To induce the Note A Lenders to make Loan A and the Note B Lenders to make Loan B and for other valuable consideration, the Guarantor agrees as follows:

1.          Guaranteed Obligations . The Guarantor absolutely and unconditionally guarantees the punctual and complete payment and performance when due of all indebtedness and obligations of Borrower under that certain Environmental Indemnification Agreement #1 dated of even date herewith and that certain Environmental Indemnification Agreement #2 dated of even date herewith, each executed by Borrower (hereinafter, as they may be from time to time amended, modified, extended, renewed, refinanced, substituted and/or supplemented, collectively referred to as the " Environmental Indemnification Agreements "), and all other indebtedness and obligations under the Loan Documents for which Borrower has personal liability to Lender, as the same may be limited under Section 26 of Note A or Section 26 of Note B; in each case as such indebtedness and obligations may from time to time be supplemented, modified, amended, renewed and extended, whether evidenced by new or additional instruments, documents or agreements or otherwise (collectively, the " Guaranteed Obligations "). Without limiting the foregoing, upon the occurrence of any of the events described in Subsections 26(j) and 26(l) of Note A and Subsections 26(j) and 26(l) of Note B, the limitation on the recourse of Lender against Borrower shall be null and void and Lender shall have full recourse against Borrower for, and the Guarantor shall jointly and severally guaranty the payment and performance by Borrower of, Loan A, Loan B and all principal, interest and other sums owing under Note A, Note B or any of the other Loan Documents (as defined in the Agreement) (all such documents, collectively, the " Loan Documents "). Upon the occurrence of any Event of Default, all Guaranteed Obligations shall, at the option of Collateral Agent, immediately become due and payable by the Guarantor without protest, presentment, notice of dishonor, demand or further notice of any kind, all of which are expressly waived by the Guarantor, and irrespective of whether any Guaranteed Obligations have then become due and payable by the Borrower or any other Person (each of the Borrower and any such other Person other than Guarantor being referred to in this Guaranty as an " other Borrower Party ").

2.          Nature of Guaranty . This Guaranty is a guaranty of payment and performance and not of collection, is continuing in nature and applies to all Guaranteed Obligations, whether existing now or in the future, including (a) interest and other Guaranteed Obligations arising or accruing after bankruptcy of any other Borrower Party or any sale or other disposition of any security for this Guaranty or for the obligations of any other Borrower Party (any such security being referred to in this Guaranty as the " Security "), and (b) any Guaranteed Obligations that survive repayment of the Loans. This Guaranty and any Security for this Guaranty shall continue to be effective or be reinstated, as the case may be, if at any time any payment or performance of any Guaranteed Obligations is rescinded or must otherwise be

returned by Collateral Agent, the Note A Lenders, the Note B Lenders or any other Person upon the bankruptcy, insolvency or reorganization of any other Borrower Party or otherwise, all as though such payment or performance had not occurred. The Guarantor shall have no authority to revoke this Guaranty, but if any such revocation shall be deemed to have occurred by operation of law or otherwise, the provisions of this Guaranty shall continue to apply notwithstanding such revocation.

3.          Obligations Independent . The obligations of the Guarantor under this Guaranty are independent of the obligations of any other Borrower Party under the Loan Documents (such obligations of any other Borrower Party, including the Borrower's obligations in respect of the Guaranteed Obligations, being referred to in this Guaranty as the " Other Obligations ") and any Security, and the enforceability of any Security for this Guaranty is likewise independent of any such Other Obligations and any other Security. Collateral Agent may bring action against the Guarantor and otherwise enforce this Guaranty or any Security for this Guaranty without bringing action against any other Borrower Party or joining any other Borrower Party in any action against the Guarantor, and otherwise independently of any other right, power or remedy (each, a " Remedy ") that may be available to Lender at any time with respect to any Other Obligations or Security. The Guarantor waives any right to require Collateral Agent or Lenders at any time to proceed against any other Borrower Party, apply any Security or otherwise enforce, proceed against or exhaust any Other Obligations or Security or pursue any other Remedy in Collateral Agent's or any Lender's power.

4.          Action with Respect to Other Obligations or Security . The Guarantor authorizes Collateral Agent and each Lender, without notice or demand and without affecting its liability under or the enforceability of this Guaranty or any Security for this Guaranty, from time to time to:

(a)       supplement, modify, amend, renew, extend, accept partial payments or performance on or otherwise change the time, manner or place of payment or performance or the interest rate or other terms or the amount of, or release, reconvey, terminate, waive, abandon, subordinate, exchange, substitute, transfer or consent to the transfer of or enter into or give any other agreement, approval, waiver or consent with respect to or in exchange for any Other Obligations or Security or any of the Loan Documents (including release the Fourteenth Floor (as defined in Note B) pursuant to Section 29 of Note A or Section 29 of Note B);

(c)       release any other Borrower Party from any personal liability with respect to any Other Obligations and participate in any bankruptcy or reorganization of any other Borrower Party in such manner as Collateral Agent or such Lender may determine; and

(d)       accelerate, settle, compromise, compound, sue for, collect or otherwise liquidate, enforce or deal with any Other Obligations or Security (including judicial or nonjudicial sale or other disposition of any Security), bid and purchase at any sale or other disposition of any Security and apply any Security and any proceeds or other

payments received by Collateral Agent or such Lender, in each case in such order and manner as Collateral Agent or such Lender may determine.

5.          Waiver of Defenses . The Guarantor waives any defense to the enforcement of this Guaranty or any Security for this Guaranty arising by reason of:

(a)       any present or future federal, state or local laws, rules, regulations, ordinances or codes (all such laws, rules, regulations, ordinances or codes being hereinafter referred to collectively as " Laws "), or orders affecting the terms of, or Collateral Agent's or any Lender's Remedies with respect to, any Other Obligations or Security;

(b)       the absence or cessation of personal liability of any other Borrower Party with respect to any Other Obligations;

(c)       the failure of any other Person to execute this Guaranty or any other guaranty or agreement;

(d)       the failure of any other Borrower Party to properly execute any Loan Document or otherwise comply with applicable legal formalities;

(e)       the unenforceability or invalidity of any Other Obligations or Security or the lack of perfection or failure of priority or any other loss or impairment of any Security;

(f)        any discharge or release of any other Borrower Party or any Other Obligations or Security or any impairment or suspension of any Remedies of Collateral Agent or any Lender, whether resulting from any act or omission of Collateral Agent or any Lender or any other Person or by operation of law or otherwise;

(g)       any bankruptcy, insolvency or reorganization of any other Borrower Party or any disability or other defense of any other Borrower Party with respect to any Other Obligations or Security;

(h)       any failure of Collateral Agent or any Lender to disclose to the Guarantor any information relating to the financial condition, operations, properties or prospects of, or any other matter relating to, any other Borrower Party now or in the future known to Collateral Agent or any Lender (the Guarantor waiving any duty on the part of Collateral Agent or any Lender to disclose such information, including in response to any request by the Guarantor to provide such information);

(i)        any failure of Collateral Agent or any Lender to monitor proper application of loan funds or compliance with the Loan Documents, or to preserve, insure or protect any Security or any subrogation, contribution or reimbursement rights of the Guarantor;

(j)        any future extensions of credit to the Borrower or any other Borrower Party;

(k)       any failure, omission or delay in the exercise or enforcement by Collateral Agent or any Lender of any Remedy against any other Borrower Party or any Security;

(l)        any application of proceeds or payments received by Collateral Agent or any Lender to obligations other than the Guaranteed Obligations; or

(m)      any other action by Collateral Agent or any Lender, whether authorized by Section 4 of this Guaranty or otherwise, or any omission by Collateral Agent or any Lender or other failure of Collateral Agent or any Lender to pursue, or any delay in pursuing, any other Remedy in Collateral Agent's or any Lender's power.

The Guarantor further waives: (i) any defense to the recovery by Collateral Agent or any Lender against the Guarantor of any deficiency or otherwise to the enforcement of this Guaranty or any Security for this Guaranty based upon the Collateral Agent's or any Lender's election of any remedy against Guarantor or any other Borrower Party; (ii) any defense or benefits that may be derived from any anti-deficienc