Exhibit 10.6

PARTIAL RELEASE AND ACKNOWLEDGEMENT AGREEMENT

This Partial Release and Acknowledgment Agreement (the “Agreement”) is entered
into as of September 27, 2006, by and among (i) SILICON VALLEY BANK, a
California chartered bank, with its principal place of business at 3003 Tasman
Drive, Santa Clara, California 95054 and with a loan production office located
at One Newton Executive Park, Suite 200, 2221 Washington Street, Newton,
Massachusetts  02462 (“SVB”), (ii) ASPEN TECHNOLOGY, INC., a Delaware
corporation with offices at Ten Canal Park, Cambridge, Massachusetts 02141, for
itself and as successor by merger to ASPENTECH, INC., formerly a Texas
corporation  with offices at Ten Canal Park, Cambridge, Massachusetts 02141(
“Borrower”), and the parties who have executed this Agreement, as evidenced by
their signature below (each a “Party”, and collectively, the “Parties”).

Whereas, Borrower is indebted to SVB pursuant to a loan arrangement dated as of
January 30, 2003, as evidenced by a certain Loan and Security Agreement and a
certain Export-Import Bank Loan and Security Agreement each dated as of January
30, 2003 (each as amended and in effect, collectively, the “SVB Loan
Arrangement”) and SVB and Borrower have also entered into a certain Non-Recourse
Receivables Purchase Agreement dated December 31, 2003 (as amended and in
effect, the “SVB Purchase Facility”).

Whereas, SVB has agreed to release its security interest in certain assets of
Borrower in accordance with the provisions hereof in order to permit Borrower to
sell such assets to Aspen Technology Funding 2006 - I LLC, free and clear of the
security interest granted to SVB under the SVB Loan Arrangement and SVB’s
interest in the accounts receivable purchased under the SVB Purchase Facility,
which assets shall be subsequently conveyed by Aspen Technology Funding 2006 - I
LLC to Aspen Technology Funding 2006 - II LLC (“SPE II”), and which assets will
then be pledged by SPE II to Key Equipment Finance, Inc., as agent for certain
lenders extending loans to SPE II (the “Key Transaction”).

Now, therefore, for good and valuable consideration, the receipt and sufficiency
of which are hereby acknowledged, SVB, the Borrower, and the Parties hereby
agree as follows:

1.             PARTIAL RELEASE.  SVB HEREBY IRREVOCABLY RELEASES ANY LIEN,
CLAIM, ENCUMBRANCE OR SECURITY INTEREST (INCLUDING, WITHOUT LIMITATION, ITS
SECURITY INTERESTS UNDER THE SVB LOAN ARRANGEMENT AND ITS INTEREST IN ACCOUNTS
RECEIVABLE PURCHASED UNDER THE SVB PURCHASE FACILITY) IT MAY HAVE, SOLELY IN
THOSE CERTAIN ACCOUNTS RECEIVABLE, CONTRACTS (OR PORTION THEREOF), RELATED
SECURITY, AND COLLECTIONS WHICH ARE LISTED ON EXHIBIT A HERETO (THE “SPV
RECEIVABLES”) AND ALL PROCEEDS THEREOF.

2.             TREATMENT OF PROCEEDS OF THE SPV RECEIVABLES.   SVB SPECIFICALLY
ACKNOWLEDGES AND AGREES THAT IT SHALL RETAIN NO SECURITY INTEREST OR OWNERSHIP
INTEREST IN OR TO THE SPV RECEIVABLES OR THE PROCEEDS THEREOF (THE “FUNDS”).  IN
THE EVENT SVB RECEIVES, ACQUIRES OR OBTAINS ANY SUCH FUNDS DIRECTLY FROM THE
COLLECTION ACCOUNT (AS DEFINED HEREIN) AS

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payment of any of the Borrower’s obligations under the SVB Loan Arrangement or
the SVB Purchase Facility, in connection with a disbursement request by the
Borrower to SVB directly from the Collection Account, or by set off or other
action taken by SVB against the Collection Account, SVB agrees to promptly turn
over any such Funds, or the proceeds thereof, to KEY or, at SVB’s option, SVB
may deposit such Funds into a court of competent jurisdiction in an interpleader
action.  In the event that any Party receives, acquires or obtains any
collateral or property of SVB, such Party hereby agrees to promptly turn over
such collateral, property, or the proceeds thereof, to SVB, or, at Key’s option,
Key may deposit such Funds into a court of competent jurisdiction in an
interpleader action.

3.             AMENDMENT TO UCC FINANCING STATEMENT.  UPON RECEIPT OF THIS FULLY
EXECUTED AGREEMENT, SVB SHALL FILE THE FOLLOWING UCC FINANCING STATEMENTS ON
BEHALF OF SVB, AS SECURED PARTY:

(A)                                  AMENDMENT TO FINANCING STATEMENT, RELEASING
SVB’S SECURITY INTEREST IN THE SPV RECEIVABLES AND THE PROCEEDS THEREOF, NAMING
ASPEN TECHNOLOGY, INC., AS DEBTOR, IN THE FORM OF EXHIBIT B HERETO, TO BE FILED
WITH THE DELAWARE SECRETARY OF STATE; AND

(B)                                 AMENDMENT TO FINANCING STATEMENT, RELEASING
SVB’S SECURITY INTEREST IN THE SPV RECEIVABLES AND THE PROCEEDS THEREOF, NAMING
ASPENTECH, INC., AS DEBTOR, IN THE FORM OF EXHIBIT C HERETO, TO BE FILED WITH
THE TEXAS SECRETARY OF STATE.

SVB agrees to deliver any such UCC financing statement partial releases
reasonably requested by Aspen or Key to effectuate the terms of paragraphs 1 and
3 hereof.

4.             ACKNOWLEDGEMENT.  THE BORROWER MAINTAINS A LOCKBOX WITH SVB
IDENTIFIED AS FOLLOWS: “ASPEN TECHNOLOGY INC. BOX 83048, WOBURN, MA 01813-3048”
(THE “LOCKBOX ACCOUNT”).  THE LOCKBOX ACCOUNT PROCEEDS ARE CURRENTLY TRANSFERRED
DIRECTLY TO A COLLECTION ACCOUNT MAINTAINED AT SVB IN THE NAME OF ASPEN
TECHNOLOGY, INC. IDENTIFIED AS ACCOUNT NO. 3300388202 (THE “ DOMESTIC COLLECTION
ACCOUNT”).   IN ADDITION, CERTAIN WIRES ARE TRANSFERRED TO A SEPARATE COLLECTION
ACCOUNT MAINTAINED AT SVB IN THE NAME OF ASPEN TECHNOLOGY, INC. IDENTIFIED AS
ACCOUNT NO. 3300388217 (COLLECTIVELY WITH THE DOMESTIC COLLECTION ACCOUNT, THE
“COLLECTION ACCOUNT”).  SVB ACKNOWLEDGES THAT THE BORROWER AND KEY HAVE ADVISED
SVB THAT SPE II SHALL, UPON ACQUISITION OF INTERESTS IN THE SPV RECEIVABLES,
GRANT OR HAS GRANTED KEY A SECURITY INTEREST IN THE SPV RECEIVABLES AND THE
PROCEEDS THEREOF, AND THAT THE LOCKBOX ACCOUNT AND THE COLLECTION ACCOUNT MAY
CONTAIN CERTAIN OR ALL OF THE FUNDS, WHICH ARE THE PROCEEDS OF THE SPV
RECEIVABLES.

5.             ENTIRE AGREEMENT.  THIS AGREEMENT (INCLUDING EXHIBITS HERETO)
SETS FORTH THE ENTIRE AGREEMENT BETWEEN THE PARTIES WITH RESPECT TO THE SUBJECT
MATTER HEREOF, AND SUPERSEDES ALL PRIOR NEGOTIATIONS, UNDERSTANDINGS AND
AGREEMENTS BETWEEN THE PARTIES CONCERNING SUCH SUBJECT MATTER.  NO AMENDMENT OR
MODIFICATION OF THIS AGREEMENT SHALL

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be effective against a Party except by a writing signed by authorized
representative of such Party.

6.             NO RESPONSIBILITY/INDEMNIFICATION.  (A)  THE BORROWER AND THE
PARTIES SIGNING BELOW CONFIRM AND AGREE:

(I)                                     THAT SVB IS NOT UNDERTAKING TO TAKE ANY
ACTION WITH RESPECT TO THE LOCKBOX ACCOUNT, OR COLLECTION ACCOUNT, EXCEPT AS SET
FORTH IN THE AGREEMENTS BETWEEN SVB AND THE BORROWER PERTAINING THERETO, AND
EXCEPT AS PROVIDED HEREIN.

(II)                                  THAT SVB SHALL NOT HAVE ANY DUTIES OR
RESPONSIBILITIES EXCEPT SUCH DUTIES AND RESPONSIBILITIES AS ARE SPECIFICALLY SET
FORTH IN THIS AGREEMENT AND NO COVENANTS OR OBLIGATIONS SHALL BE IMPLIED IN THIS
AGREEMENT AGAINST SVB.

(B)                                 THE BORROWER CONFIRMS AND AGREES:

(I)                                     TO INDEMNIFY SVB AND ITS DIRECTORS,
OFFICERS, EMPLOYEES AND AGENTS HARMLESS AGAINST:  (I) ALL OBLIGATIONS, DEMANDS,
CLAIMS, AND LIABILITIES ASSERTED BY ANY PARTY OR PERSON IN CONNECTION WITH THE
TRANSACTIONS CONTEMPLATED BY THIS AGREEMENT; AND (II) ALL LOSSES INCURRED, OR
PAID BY SVB FROM, FOLLOWING, OR CONSEQUENTIAL TO TRANSACTIONS RELATING TO THIS
AGREEMENT.

7.             GOVERNING LAW.  THIS AGREEMENT SHALL BE GOVERNED AND INTERPRETED
IN ACCORDANCE WITH THE LAWS OF THE COMMONWEALTH OF MASSACHUSETTS, WITHOUT REGARD
TO PRINCIPLES OF CONFLICT OF LAWS, UNDER THE LAW OF THE COMMONWEALTH OF
MASSACHUSETTS.

[Remainder of Page Intentionally Left Blank]

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In witness whereof, the parties have executed this Agreement as of the date
first written above.

 

SILICON VALLEY BANK

 

By:

/s/ Michael Tramack

 

Name:

Michael Tramack

 

Title:

Senior Vice President

 

 

 

ASPEN TECHNOLOGY, INC.

 

By:

/s/ Leo S. Vannoni

 

Name:

Leo S. Vannoni

 

Title:

Treasurer

 

 

 

AGREED AND ACKNOWLEDGED:

 

 

KEY EQUIPMENT FINANCE, INC., as agent

 

 

By:

/s/ Donald C. Davis

 

Name:

Donald C. Davis

 

Title:

Vice President

 

 

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Exhibit A

All of the Receivables, Collections and all proceeds thereof, in each case, as
more particularly described below.

“Collections” means, with respect to any Receivable, all funds paid by or on
behalf of the related obligor of such Receivable in payment of any amounts owed
(including, without limitation, purchase or sale prices, principal, finance
charges, interest and all other charges) in respect of such Receivable.

“Receivable” means all indebtedness and other obligations identified on Schedule
I  hereto (“Assets”), owed to Aspen Technology, Inc. or any affiliate thereof,
including, without limitation, any indebtedness, obligation or interest relating
to the Assets, and further including, without limitation, all rights to payment
of such indebtedness or obligation arising under the related contract with
respect to the Assets,  and the obligation to pay any finance charges with
respect to the Assets.

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