<PAGE>
                                                                    EXHIBIT 10.6
                               GUARANTY AGREEMENT


         WHEREAS, the execution of this Guaranty Agreement is a condition to
KOGER ACP, LLC, a Delaware limited liability company ("Borrower") assuming loans
from (i) METROPOLITAN LIFE INSURANCE COMPANY ("MetLife"), a New York corporation
having its principal place of business at 10 Park Avenue, Morristown, New Jersey
07960, and (ii) METLIFE BANK, N.A. ("MetLife Bank"), a national banking
association, having an address of 10 Park Avenue, Morristown, New Jersey 07960
(MetLife and MetLife Bank being collectively referred to as "Lender"), to
ATLANTIC CENTER PLAZA, LLC ("Original Borrower") in the aggregate original
principal amount of $90,000,000.00;

         NOW, THEREFORE, for valuable consideration, the receipt and adequacy of
which are hereby acknowledged, the undersigned, KOGER EQUITY, INC., a Florida
corporation ("Guarantor"), whose address is 225 NE Mizner Boulevard, Suite 200,
Boca Raton, Florida 33432-3945, hereby irrevocably and unconditionally
guarantees to Lender the full and prompt payment and performance of the
Guaranteed Obligations (as defined below), this Guaranty Agreement being upon
the following terms:

         1. The term "Indebtedness" as used herein shall mean all obligations,
indebtedness and liabilities of Borrower to any Lender evidenced by (i) that
certain Promissory Note dated December 30, 2003, made by Atlantic Center Plaza,
LLC to the order of Metropolitan Life Insurance Company in the principal face
amount of $74,000,000.00, (ii) that certain Promissory Note dated December 30,
2003, made by Atlantic Center Plaza, LLC to the order of Metropolitan Life
Insurance Company in the principal face amount of $9,000,000.00, (iii) that
certain Promissory Note dated December 30, 2003, made by Atlantic Center Plaza,
LLC to the order of MetLife Bank, N.A. in the principal face amount of
$6,000,000.00, (iv) that certain Promissory Note dated December 30, 2003, made
by Atlantic Center Plaza, LLC to the order of MetLife Bank, N.A. in the
principal face amount of $1,000,000.00 (the foregoing described Promissory Notes
in (i) through (iv) above being collectively referred to as the "Note" or
"Notes"), (v) the other Loan Documents (as defined in the Notes) and (vi) the
Unsecured Indemnity Agreement (as defined in the Notes), all as said Notes, Loan
Documents and Unsecured Indemnity Agreement have been assumed by the Borrower
pursuant to that certain Assumption and Modification Agreement dated as of even
date among Metropolitan Life Insurance Company, MetLife Bank, N.A., Koger ACP,
LLC, Koger Equity, Inc., Atlantic Center Plaza, LLC, Lawrence P. Kelly, and A.J.
Land, Jr. (the "Assumption Agreement").

         2. The term "Guaranteed Obligations" as used herein means: (a) payment
and performance by Borrower of all of Borrower's liability under: (i) the
Unsecured Indemnity Agreement, as assumed pursuant to the Assumption Agreement,
and (ii) Paragraph 11 of the Notes, as assumed pursuant to the Assumption
Agreement (such amounts under subsections (i) and (ii) of this Section 2(a)
being herein called the "Performance Sums") PLUS (b) interest at the Default
Rate (as defined in the Notes) which accrues on the Performance Sums from the
date of written demand for payment under this Guaranty Agreement from Lender to
Guarantor until the Performance Sums are paid in full PLUS (c) all costs,
including, without limitation, all reasonable attorney's fees and expenses
incurred by Lender in connection with collection of the Guaranteed Obligations.

         3. This instrument is an absolute, continuing, irrevocable, and
unconditional guaranty of payment and performance, and not a guaranty of
collection, and Guarantor shall remain liable on its obligations hereunder until
the payment and performance in full of the Guaranteed Obligations. No set-off,
counterclaim, recoupment, reduction, or diminution of any obligation, or any
defense of any kind or nature which Borrower may have against Lender or any
other party, or which Guarantor may have against Borrower, Lender, or any other
party, shall be available to, or shall be asserted by, Guarantor against Lender
or any subsequent beneficiary of this Guaranty Agreement or any portion of the
Indebtedness other than complete payment and performance in full of the
Guaranteed Obligations.




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         4. If Guarantor becomes liable for any indebtedness owing by Borrower
to Lender by endorsement or otherwise, other than under this Guaranty Agreement,
such liability shall not be in any manner impaired or affected hereby, and the
rights of Lender hereunder shall be in addition to any and all other rights that
Lender may ever have against Guarantor. The exercise by Lender of any right or
remedy hereunder or under any other instrument, or at law or in equity, shall
not preclude the concurrent or subsequent exercise of any other right or remedy.

         5. In the event of default by Borrower in payment or performance of the
Guaranteed Obligations, or any part thereof, when such Guaranteed Obligations
are due to be paid or performed by Borrower, Guarantor shall promptly pay or
perform the Guaranteed Obligations then due in full without notice or demand,
and it shall not be necessary for Lender, in order to enforce such payment by
Guarantor, first to institute suit or exhaust its remedies against Borrower or
others, or to enforce any rights against any collateral which shall ever have
been given to secure such Indebtedness. Without limiting any other provisions of
this Guaranty Agreement, Guarantor acknowledges and agrees that, to the extent
Lender realizes any proceeds under any documents which secure the Indebtedness
(including, without limitation, voluntary payments, insurance or condemnation
proceeds or proceeds from the sale at foreclosure of any collateral securing the
Indebtedness), such proceeds shall, to the extent permitted by law, not be
applied to or credited against the Guaranteed Obligations. FURTHER,
NOTWITHSTANDING ANYTHING TO THE CONTRARY CONTAINED IN THIS GUARANTY AGREEMENT,
GUARANTOR HEREBY IRREVOCABLY AGREES THAT, UNTIL PAYMENT IN FULL TO LENDER OF THE
INDEBTEDNESS AND THE GUARANTEED OBLIGATIONS, GUARANTOR SHALL HAVE NO RIGHT TO
RECOVER FROM BORROWER ANY CLAIMS GUARANTOR HAS OR MIGHT HAVE AGAINST BORROWER
(AS SUCH TERM "CLAIM" IS DEFINED IN THE UNITED STATES BANKRUPTCY CODE 11 U.S.C.
SS.101[5] AS AMENDED FROM TIME TO TIME) IN CONNECTION WITH PAYMENTS MADE BY OR
ON BEHALF OF GUARANTOR TO LENDER UNDER THIS GUARANTY AGREEMENT INCLUDING,
WITHOUT IMPLIED LIMITATION, ALL RIGHTS GUARANTOR MAY NOW OR HEREAFTER HAVE UNDER
ANY AGREEMENT OR AT LAW OR IN EQUITY (INCLUDING, WITHOUT LIMITATION, ANY LAW
SUBROGATING THE GUARANTOR TO THE RIGHTS OF LENDER) TO ASSERT ANY CLAIM AGAINST
OR SEEK CONTRIBUTION, INDEMNIFICATION OR ANY OTHER FORM OF REIMBURSEMENT FROM
BORROWER OR ANY OTHER PARTY LIABLE FOR PAYMENT OF ANY OR ALL OF THE
INDEBTEDNESS.

         6. If acceleration of the time for payment by Borrower of all or any
portion of the Indebtedness is stayed upon the insolvency, bankruptcy, or
reorganization of Borrower, the Guaranteed Obligations shall nonetheless be
payable by Guarantor hereunder forthwith on demand by Lender.

         7. Guarantor hereby agrees that its obligations under this Guaranty
Agreement shall not be released, discharged, diminished, impaired, reduced, or
affected for any reason or by the occurrence of any event, including, without
limitation, one or more of the following events, whether or not with notice to
or the consent of Guarantor: (a) the taking or accepting of collateral as
security for any or all of the Indebtedness or the release, surrender, exchange,
or subordination of any collateral now or hereafter securing any or all of the
Indebtedness; (b) the full or partial release of Borrower or any other guarantor
from liability for any or all of the Indebtedness or the Guaranteed Obligations;
(c) the dissolution, insolvency, or bankruptcy of Borrower, Guarantor, or any
other party at any time liable for the payment of any or all of the
Indebtedness; (d) any renewal, extension, modification, waiver, amendment, or


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rearrangement of any or all of the Indebtedness or any instrument, document, or
agreement evidencing, securing, or otherwise relating to any or all of the
Guaranteed Obligations; (e) any adjustment, indulgence, forbearance, waiver, or
compromise that may be granted or given by Lender to Borrower or any other party
ever liable for any or all of the Indebtedness; (f) any neglect, delay,
omission, failure, or refusal of Lender to take or prosecute any action for the
collection of any of the Guaranteed Obligations from Borrower or Guarantor or to
foreclose or take or prosecute any action in connection with any instrument,
document, or agreement evidencing, securing, or otherwise relating to any or all
of the Indebtedness or any or all of the Guaranteed Obligations; (g) the
unenforceability or invalidity of any or all of the Indebtedness or the
Guaranteed Obligations or any instrument, document, or agreement evidencing,
securing, or otherwise relating to any or all of the Indebtedness or the
Guaranteed Obligations; (h) any payment by Borrower or any other party to Lender
is held to constitute a preference under applicable bankruptcy or insolvency law
or if for any other reason Lender is required to refund any payment or pay the
amount thereof to someone else; (i) the settlement or compromise of any of the
Indebtedness or the Guaranteed Obligations; (j) the non-perfection of any
security interest or lien securing any or all of the Indebtedness; (k) any
impairment of any collateral securing any or all of the Indebtedness; (l) the
failure of Lender to sell any collateral securing any or all of the Indebtedness
in a commercially reasonable manner or as otherwise required by law; (m) any
change in the corporate existence, structure, or ownership of Borrower; (n) the
application against the Indebtedness of the proceeds realized by Lender under
any documents which secure the Indebtedness (including, without limitation,
voluntary payments, insurance or condemnation proceeds or proceeds from the sale
at foreclosure of any collateral securing the Indebtedness), except as provided
in Section 5 of this Guaranty Agreement; or (o) any other circumstance which
might otherwise constitute a defense available to, or discharge of, Borrower or
Guarantor, or any other party liable for any or all of the Indebtedness or the
Guaranteed Obligations. Guarantor further expressly waives any right or option
under applicable law or otherwise to be released or discharged, in whole or in
part, by reason of any of the matters set forth in (a) through (o) of this
Section, and further expressly waives any defense to the full payment and
performance of the Guaranteed Obligations arising from the matters set forth in
(a) through (o) of this Section. In addition, Guarantor expressly waives: (i)
any duty or obligation on the Lender to proceed to collect payment of the
Indebtedness from, or to commence an action against, the Borrower or any other
person, or to resort to any security or to any balance of any deposit account or
credit on the books of the Lender in favor of the Borrower or any other person,
despite any notice or request of the undersigned to do so; and (ii) any and all
rights Guarantor may have under Georgia Code Section 10-7-24 and Georgia Code
Section 44-14-161 (it being intended that Guarantor shall be primarily liable
hereunder notwithstanding Lender's failure to confirm any foreclosure sale
pursuant to said provision).

        8. Guarantor represents and warrants to Lender as follows:

                  (a) Guarantor has the power and authority and legal right to
execute, deliver, and perform its obligations under this Guaranty Agreement and
this Guaranty Agreement constitutes the legal, valid, and binding obligation of
Guarantor, enforceable against Guarantor in accordance with its terms, except as
limited by bankruptcy, insolvency, or other laws of general application relating
to the enforcement of creditor's rights.

                  (b) The execution, delivery, and performance by Guarantor of
this Guaranty Agreement do not and will not violate or conflict with any law,
rule, or regulation or any order, writ, injunction, or decree of any court,
governmental authority or agency, or arbitrator and do not and will not conflict
with, result in a breach of, or constitute a default under, or result in the
imposition of any lien upon any assets of Guarantor pursuant to the provisions
of any indenture, mortgage, deed of trust, security agreement, franchise,
permit, license, or other instrument or agreement to which Guarantor or his
properties are bound.

                  (c) No authorization, approval, or consent of, and no filing
or registration with, any court, governmental authority, or third party is
necessary for the execution, delivery, or performance by Guarantor of this
Guaranty Agreement or the validity or enforceability thereof.

                  (d) The value of the consideration received and to be received
by Guarantor as a result of Lender making extensions of credit to Borrower and
Guarantor executing and delivering this Guaranty Agreement is reasonably worth
at least as much as the liability and obligation of Guarantor hereunder, and


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such liability and obligation and such extensions of credit have benefited and
may reasonably be expected to benefit Guarantor directly and indirectly.

                  (e) Guarantor has, independently and without reliance upon
Lender and based upon such documents and information as Guarantor has deemed
appropriate, made its own analysis and decision to enter into this Guaranty
Agreement.

         9. Guarantor covenants and agrees that, as long as the Indebtedness or
the Guaranteed Obligations or any part thereof is outstanding:

                  (a) Guarantor will furnish to Lender as soon as available, and
in any event within ninety (90) days after the end of each fiscal year of
Guarantor, beginning with the fiscal year ending December 31, 2003, (i) a copy
of the financial statements of Guarantor for such fiscal year and (ii) a
certificate of Guarantor to Lender (A) stating that no default under this
Guaranty Agreement and no event which with notice or lapse of time or both would
be a default under this Guaranty Agreement has occurred and is continuing, or if
in Guarantor's opinion a default under this Guaranty Agreement has occurred and
is continuing, a statement as to the nature thereof and (B) disclosing and
certifying as to all material changes in Guarantor's debt or net worth or
otherwise certifying that there has been no material change in Guarantor's
personal debt or net worth since the previous financial statement delivered to
Lender.

                  (b) Guarantor will furnish promptly to Lender written notice
of the occurrence of any default under this Guaranty Agreement.

                  (c) Guarantor will furnish promptly to Lender such additional
information concerning Guarantor as Lender may reasonably request.

                  (d) Guarantor will obtain at any time and from time to time
all authorizations, licenses, consents or approvals as shall now or hereafter be
necessary or desirable under all applicable laws or regulations or otherwise in
connection with the execution, delivery and performance of this Guaranty
Agreement and will promptly furnish copies thereof to Lender.

                  (e) Except for transfers permitted under the Notes and the
other Loan Documents, Guarantor will at all times own directly or indirectly and
free and clear of all liens and encumbrances whatsoever at least the same
percentage interest in Borrower, if any, as it owns directly or indirectly on
the date hereof.

         10. (a) From and after the occurrence of an Event of Default (as
defined in the Notes), Guarantor hereby agrees that the Subordinated
Indebtedness (as hereinafter defined) shall be subordinate and junior in right
of payment to the prior payment in full of all Indebtedness, and Guarantor
hereby assigns the Subordinated Indebtedness to Lender as security for the
payment of the Guaranteed Obligations. If any sums shall be paid to Guarantor by
Borrower or any other person or entity on account of the Subordinated
Indebtedness, such sums shall be held in trust by Guarantor for the benefit of
Lender and shall forthwith be paid to Lender without affecting the liability of


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Guarantor under this Guaranty Agreement and may be applied by Lender against the
Indebtedness or the Guaranteed Obligations in such order and manner as Lender
may determine in its sole discretion. Upon the request of Lender, Guarantor
shall execute, deliver, and endorse to Lender such documents and instruments as
Lender may request to perfect, preserve, and enforce its rights hereunder. For
purposes of this Guaranty Agreement, the term "Subordinated Indebtedness" means
all indebtedness, liabilities, and obligations of Borrower to Guarantor, whether
such indebtedness, liabilities, and obligations now exist or are hereafter
incurred or arise, or whether the obligations of Borrower thereon are direct,
indirect, contingent, primary, secondary, several, joint and several, or
otherwise, and irrespective of whether such indebtedness, liabilities, or
obligations are evidenced by a note, contract, open account, or otherwise, and
irrespective of the person or persons in whose favor such indebtedness,
obligations, or liabilities may, at their inception, have been, or may hereafter
be created, or the manner in which they have been or may hereafter be acquired
by Guarantor; provided, however, that the term "Subordinated Indebtedness" shall
not mean or include any distributions by Borrower to its members pursuant to the
operating agreement of Borrower at any time when no Event of Default exists.

                  (b) Guarantor agrees that any and all liens, security
interests, judgment liens, charges, or other encumbrances upon Borrower's assets
securing payment of any Subordinated Indebtedness shall be and remain inferior
and subordinate to any and all liens, security interests, judgment liens,
charges, or other encumbrances upon Borrower's assets securing payment of the
Indebtedness or any part thereof, regardless of whether such encumbrances in
favor of Guarantor or Lender presently exist or are hereafter created or
attached. Without the prior written consent of Lender until the Indebtedness has
been paid in full, Guarantor shall not (i) file suit against Borrower or
exercise or enforce any other creditor's right it may have against Borrower, or
(ii) foreclose, repossess, sequester, or otherwise take steps or institute any
action or proceedings (judicial or otherwise, including without limitation the
commencement of, or joinder in, any liquidation, bankruptcy, rearrangement,
debtor's relief or insolvency proceeding) to enforce any liens, security
interests, collateral rights, judgments or other encumbrances held by Guarantor
on assets of Borrower.

                  (c) In the event of any receivership, bankruptcy,
reorganization, rearrangement, debtor's relief, or other insolvency proceeding
involving Borrower as debtor, Lender shall have the right to prove and vote any
claim under the Subordinated Indebtedness and to receive directly from the
receiver, trustee or other court custodian all dividends, distributions, and
payments made in respect of the Subordinated Indebtedness. Lender may apply any
such dividends, distributions, and payments against the Guaranteed Obligations
in such order and manner as Lender may determine in its sole discretion.
Guarantor hereby appoints Lender as Guarantor's attorney-in-fact, which
appointment is coupled with an interest and is irrevocable, to enable Lender to
act in the place of Guarantor with respect to (i) any claim under the
Subordinated Indebtedness or (ii) the receipt of any such dividends,
distributions and payments.

                  (d) Guarantor agrees that all promissory notes, accounts
receivable, ledgers, records, or any other evidence of Subordinated Indebtedness
shall contain a specific written notice thereon that the indebtedness evidenced
thereby is subordinated under the terms of this Guaranty Agreement.

         11. No amendment or waiver of any provision of this Guaranty Agreement
nor consent to any departure by the Guarantor therefrom shall in any event be
effective unless the same shall be in writing and signed by Lender. No failure
on the part of Lender to exercise, and no delay in exercising, any right, power,
or privilege hereunder shall operate as a waiver thereof; nor shall any single
or partial exercise of any right, power, or privilege hereunder preclude any
other or further exercise thereof or the exercise of any other right, power, or
privilege. The remedies herein provided are cumulative and not exclusive of any
remedies provided by law.

         12. Any acknowledgment or new promise, whether by payment of principal
or interest or otherwise and whether by Borrower or others (including
Guarantor), with respect to any of the Indebtedness shall, if the statute of
limitations in favor of Guarantor against Lender shall have commenced to run,
toll the running of such statute of limitations and, if the period of such
statute of limitations shall have expired, prevent the operation of such statute
of limitations.

         13. This Guaranty Agreement is for the benefit of Lender and its
successors and assigns, and in the event of an assignment of the Indebtedness,
or any part thereof, the rights and benefits hereunder, to the extent applicable
to the portion of the Indebtedness so assigned, may be transferred with such
Indebtedness. This Guaranty Agreement is binding not only on Guarantor, but on
Guarantor's successors and assigns.



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         14. Guarantor recognizes that Lender is relying upon this Guaranty
Agreement and the undertakings of Guarantor hereunder in making extensions of
credit to Borrower and further recognizes that the execution and delivery of
this Guaranty Agreement is a material inducement to Lender in making extensions
of credit to Borrower. Guarantor hereby acknowledges that there are no
conditions to the full effectiveness of this Guaranty Agreement.

         15. This Guaranty Agreement is executed and delivered as an incident to
a lending transaction negotiated, consummated, and performable in Fulton County,
Georgia, and shall be governed by and construed in accordance with the laws of
the State of Georgia. Any action or proceeding against Guarantor under or in
connection with this Guaranty Agreement may be brought in any state court in
Fulton County, Georgia or in any federal court in Fulton County or Atlanta,
Georgia. Guarantor hereby irrevocably (i) submits to the nonexclusive
jurisdiction of such courts, and (ii) waives any objection it may now or
hereafter have as to the venue of any such action or proceeding brought in such
court or that such court is an inconvenient forum. Guarantor agrees that service
of process and/or notice upon it may be made by certified or registered mail,
return receipt requested, at its address specified on the first page hereof.
Nothing herein shall affect the right of Lender to serve process in any other
matter permitted by law or shall limit the right of Lender to bring any action
or proceeding against Guarantor or with respect to any of Guarantor's property
in courts in other jurisdictions. Any action or proceeding by Guarantor against
Lender shall be brought only in a court located in Fulton County, Georgia or in
any federal court in Fulton County or Atlanta, Georgia.

         16. Guarantor hereby waives promptness, diligence, notice of any
default under the Indebtedness or of Borrower's failure to pay or perform the
Guaranteed Obligations, demand of payment, notice of acceptance of this Guaranty
Agreement, presentment, notice of protest, notice of dishonor, notice of the
incurring by Borrower of additional indebtedness, and all other notices and
demands with respect to the Indebtedness and this Guaranty Agreement.

         17. Guarantor hereby represents and warrants to Lender that Guarantor
has adequate means to obtain from Borrower on a continuing basis information
concerning the financial condition and assets of Borrower and that Guarantor is
not relying upon Lender to provide (and Lender shall have no duty to provide)
any such information to Guarantor either now or in the future.

         18. In case any one or more of the provisions contained in this
Guaranty Agreement shall for any reason be held to be invalid, illegal or
unenforceable in any respect, such invalidity, illegality or unenforceability
shall not affect any other provision hereof, and this Guaranty Agreement shall
be construed as if such invalid, illegal or unenforceable provision had never
been contained herein.

         19. THIS GUARANTY AGREEMENT EMBODIES THE FINAL, ENTIRE AGREEMENT OF
PAYMENT AND PERFORMANCE OF GUARANTOR AND LENDER WITH RESPECT TO GUARANTOR'S
GUARANTY OF THE GUARANTEED OBLIGATIONS AND SUPERSEDES ANY AND ALL PRIOR
COMMITMENTS, AGREEMENTS, REPRESENTATIONS, AND UNDERSTANDINGS, WHETHER WRITTEN OR
ORAL, RELATING TO THE SUBJECT MATTER HEREOF. THIS GUARANTY AGREEMENT IS INTENDED
BY GUARANTOR AND LENDER AS A FINAL AND COMPLETE EXPRESSION OF THE TERMS OF THE
GUARANTY AGREEMENT, AND NO COURSE OF DEALING BETWEEN GUARANTOR AND LENDER, NO
COURSE OF PERFORMANCE, NO TRADE PRACTICES, AND NO EVIDENCE OF PRIOR,
CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OR DISCUSSIONS OR OTHER EXTRINSIC
EVIDENCE OF ANY NATURE SHALL BE USED TO CONTRADICT, VARY, SUPPLEMENT OR MODIFY
ANY TERM OF THIS GUARANTY AGREEMENT. THERE ARE NO ORAL AGREEMENTS BETWEEN
GUARANTOR AND LENDER.


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         EXECUTED under seal effective as of January 27, 2004.

                                           GUARANTOR:


                                           KOGER EQUITY, INC.,
                                           a Florida corporation


                                           By: /s/ Christopher L. Becker
                                               --------------------------
                                           Name:  Christopher L. Becker
                                           Title: Senior Vice President

                                           [Corporate Seal]

Signed, sealed and delivered
in the presence of:


-----------------------------------
Unofficial Witness


/s/ Barbara W. White
-----------------------------------
Notary Public

(Notarial Seal)



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