<PAGE>


Exhibit 10.106b

                                 PROMISSORY NOTE


$250,000                                                        April 11, 2003

For  valuable  consideration,  the receipt and  sufficiency  of which are hereby
acknowledged, the undersigned MICHAEL RADLOVIC ("Borrower"),  promises to pay to
the  order  of  VERTICAL  COMPUTER  SYSTEMS,   INC.,  a  California  corporation
("Lender"), in lawful money of the United States of America the principal amount
of TWO HUNDRED FIFTY  THOUSAND  Dollars  ($250,000.00  U.S.) and interest at the
rate of 10% per annum, which shall accrue from the date hereof.

1. PAYMENT OF PRINCIPAL  AND INTEREST.  Principal and interest  shall be paid as
follows:
         All principal then  outstanding,  and other amounts owing hereunder and
then unpaid shall be due and payable by April 11, 2007 (the "Maturity Date").

2. COLLATERAL AS SECURITY. This Note is secured by certain collateral, described
in the Loan and  Security  Agreement,  between  Borrower and Lender of even date
herewith (the "Security  Agreement"),  which encumbers,  among other things, the
interest of Borrower in certain assets, as more  particularly  described therein
(the  "Collateral").  This  Note,  the  Security  Agreement,  the  Stock  Pledge
Agreement  between  Borrower  and  Lender of even date  herewith,  and any other
documents  or  instruments  given  or  to be  given  to  Lender  to  secure  the
indebtedness  evidenced by this Note are collectively  referred to herein as the
"Loan Documents".

3. DEFAULT;  REMEDIES.  Each of the following  occurrences and conditions  shall
constitute  an Event of Default:  a.  failure of Borrower to pay as and when due
any money, whether principal,  interest,  or otherwise,  under this Note, or the
breach or  default  of any  obligation  to pay  money  under or  secured  by the
Security Agreement; or

         b.  failure  of  Borrower  to  perform  any  obligation  other  than an
obligation to pay money, as and when performance of such obligation is due under
this Note or Loan Documents which failure  continues for fifteen (15) days after
notice thereof from Lender to Borrower; or

         c.  failure by Borrower  to comply  with any of the terms,  provisions,
covenants,  conditions or restrictions now or hereafter affecting the Collateral
or any part thereof or contained in any  agreement  related or pertaining to the
Collateral,  which failure  continues for fifteen (15) days after notice thereof
from Lender to Borrower; or

         d.  Borrower's  making or at any time having  made any  representation,
warranty or disclosure to Lender that is or was  materially  false or misleading
on the date as of which made,  whether or not that  representation or disclosure
appears in the Loan Documents; or

                                 Promissory Note

                                     1 of 5



<PAGE>





         e. the sale,  transfer,  conveyance,  or lease of all or any portion of
the  Collateral or of any of Borrower's  rights  therein,  whether  voluntarily,
involuntarily,  or otherwise, or Borrower's entering into an agreement to do any
of the  foregoing,  in each case except as  expressly  permitted in the Security
Agreement; or

         f.  all or any  part  of the  Collateral  or any of  Borrower's  rights
therein or any other  security  for this Note at any time  being  subject to any
mortgage, deed of trust, or other encumbrance,  pledge, hypothecation,  security
interest,  or  statutory  or common law lien,  in each case except as  expressly
permitted in the Security Agreement; or

         g. if  Borrower  or any  guarantor  hereof is a  partnership,  then the
transfer  or  encumbrance  of all  or any  portion  of any  general  partnership
interest  therein,  or the  agreement  by any  general  partner to  transfer  or
encumber the same; or

         h. if  Borrower  or any  guarantor  hereof is a  corporation,  then the
transfer or encumbrance of the controlling  interest therein or the agreement by
any person controlling Borrower to transfer or encumber the same; or

         i. the occurrence of any of the following as to Borrower, any guarantor
hereof, or if either of them is a corporation,  then any parent or subsidiary of
the same,  and if either of them is a partnership,  then any general  partner of
the same  (each  and all of the  foregoing,  a  "Party")  : the  appointment  or
application for or consent to the appointment of a receiver or a trustee for any
Party or any portion of the property of any Party;  or any Party's  making of an
assignment for the benefit of its  creditors,;  or a petition being filed by any
Party pursuant to any of the provisions of the Bankruptcy Code, 11 U.S.C. ss.ss.
101 et seq., as the same may be amended, or any similar or successor statute; or
a petition being filed against any Party under the Bankruptcy  Code and the same
not being  dismissed or vacated  within  thirty (30) days after the date of such
filing;  or the attachment or  sequestration of any of the property of any Party
and the same not being  discharged  within thirty (30) days  thereafter;  or the
dissolution or termination or winding up of any Party, or the institution of any
proceeding seeking such dissolution, termination, or winding up of any Party; or

         j. N/A; or

         k. as to any lien or  encumbrance  at any time affecting any portion of
the Collateral, irrespective of priority relative to the Security Agreement, the
recording  of a notice  of  default  or the  filing of any  judicial  proceeding
seeking foreclosure thereof; or

         l. the commencement of any proceeding  seeking partition of any portion
of the Collateral.

At any time following the  occurrence of any Event of Default,  or following the
occurrence  of any event as a  consequence  of which the  obligations  evidenced
hereby may be  accelerated,  then at the election of Lender and  notwithstanding
anything to the contrary herein or elsewhere, the entire amount of principal

                                 Promissory Note

                                     2 of 5



<PAGE>





then  outstanding  under this Note and all interest,  fees,  charges,  and other
amounts  owing  and then  unpaid  hereunder  shall  become  immediately  due and
payable,  and Lender may  exercise any and all rights that it may have under the
Loan Documents, at law, in equity, and otherwise.

4.  ATTORNEYS'  FEES.  Borrower  shall pay to Lender  upon  demand all costs and
expenses  incurred by Lender in connection with  determination,  protection,  or
enforcement of any and all of Lender's rights hereunder or under any of the Loan
Documents,  including  enforcement  of  any  and  all  obligations  of  Borrower
hereunder and  thereunder  and  protection,  enhancement,  or maintenance of the
security  interests  securing such obligations or the priority of the same. Such
costs and expenses shall be payable  whether or not any suit is instituted,  and
the same shall include without limitation  attorneys' fees, expert witness fees,
costs of  investigation,  and all of such costs incurred in connection  with any
trial, appellate proceeding,  or any case or proceeding under Chapters 7, 11, or
13 of the Bankruptcy Code or any successor thereto.

5. WAIVER OF NOTICE.  Borrower and each  endorser,  guarantor and surety of this
Note  hereby  waive  diligence,  demand,  presentment  for  payment,  notice  of
discharge, notice of nonpayment, protest and notice of protest, and specifically
consent to and waive notice of any renewals or extensions of this Note,  whether
made to or in favor of Borrower or any other person or persons. 6. NOTICES.  All
notices required hereunder or pertaining hereto shall be in writing and shall be
deemed  delivered and effective upon the earlier of (i) actual receipt,  or (ii)
the date of  delivery  or refusal of the  addressee  to accept  delivery if such
notice is sent by  express  courier  service  or  United  States  mail,  postage
prepaid,  certified or registered,  return receipt requested,  in either case to
the applicable address as follows: To Borrower:

MICHAEL RADLOVIC.
330 North Indian Hill Blvd
Claremont, CA 91711

To Lender:

VERTICAL COMPUTER SYSTEMS, INC.
6336 Wilshire Boulevard
Los Angeles, CA 90048
Attn: President

Notwithstanding  the  foregoing,  any  notice  under or  pertaining  to the Loan
Documents or the  obligations  secured thereby given and effective in accordance
with  applicable  law shall be effective for purposes  hereof.  Either party may
change  the  address  at which it is to  receive  notices  hereunder  to another
business  address within the United States (but not a post office box or similar
mail  receptacle)  by giving  notice of such  change of  address  in  accordance
herewith.

                                 Promissory Note

                                     3 of 5



<PAGE>





8. EXERCISE OF RIGHTS. No single or partial exercise of any of Lenders rights or
powers  under this Note or any of the other Loan  Documents  shall  preclude any
other or further  exercise  thereof or the exercise of any other right or power.
Lender at all times  shall have the right to proceed  against any portion of the
security  which secures  payment of the  indebtedness  evidenced  hereby in such
order and manner as Lender may elect without  waiving any rights with respect to
any other portion of such  security.  Each and all rights and remedies of Lender
hereunder and under the Loan  Documents are  cumulative  and in addition to each
and all other such rights and remedies. No exercise of any right or remedy shall
preclude exercise of any other right or remedy.

9. NO WAIVER.  No failure of Lender to insist  upon  strict  performance  of any
obligation of Borrower or to exercise any right or remedy hereunder or under the
Loan Documents,  whether before or after any default,  shall  constitute or give
rise to a waiver thereof, and no waiver of any default shall constitute a waiver
of any future default or of any other default. No failure to accelerate the debt
evidenced hereby by reason of default hereunder or otherwise,  and no acceptance
of any past due  payment  hereunder  or  acceptance  of any amount less than the
amount then due, and no other indulgence that may be granted by Lender from time
to time shall (a)  preclude  the  exercise  of any right that Lender may have at
law, in equity, by contract or agreement or otherwise, or (b) constitute or give
rise to (i) a waiver of such right of acceleration or any other right, or (ii) a
novation of this Note or a reinstatement of the debt evidenced  hereby, or (iii)
any waiver of  Lender's  rights to demand and  receive  from  Borrower  full and
prompt payment and performance thereafter, to impose late charges retroactively,
or to declare a default.  Borrower and each endorser,  guarantor,  and surety of
this Note  hereby  expressly  waive the benefit of any statute or rule of law or
equity which would produce any result  contrary to or otherwise in conflict with
any of the foregoing.

10. ASSIGNMENT;  SUCCESSORS AND ASSIGNS. Lender may assign or otherwise transfer
all or any part of its interest  herein.  Promptly  following  written notice of
such  assignment  or other  transfer,  duly executed by Lender,  Borrower  shall
render full and complete performance hereunder as and when due to the transferee
so designated by Lender. Borrower shall not assign or transfer all or any of its
interests or obligations hereunder, and any attempted or purported assignment or
transfer  by  Borrower  shall be void and of no force or  effect,  except to the
extent that the same may be expressly  permitted  under the Security  Agreement.
Subject  to the  foregoing,  the terms of this Note  shall  apply to, be binding
upon,  and inure to the benefit of ail parties  hereto and their  successors and
assigns.

11.  MODIFICATION.  This Note shall not be  modified,  amended,  or  terminated,
except by written  agreement  duly  executed  and  delivered  by both Lender and
Borrower.

12.  CONFLICTS.  In the event of any conflict between any provision of this Note
and any provision of the Security Agreement, which conflict cannot reasonably be
resolved  in such a way as to give effect to all  provisions  herein and therein
contained, this Note shall govern.

                                 Promissory Note

                                     4 of 5



<PAGE>





13.  JOINT AND  SEVERAL  LIABILITY.  If this Note is  executed  by more than one
person as Borrower, then the liability Lender may of each of them shall be joint
and several.  If Borrower is a  partnership,  then the liability of each general
partner thereof hereunder shall be joint and several.

14. SEVERABILITY.  If any provision of this Note or any payments pursuant to the
terms hereof shall be invalid or unenforceable  to any extent,  the remainder of
this Note and any other  payments  hereunder  shall not be affected  thereby and
shall be enforceable to the greatest extent permitted by law.

15.  GOVERNING  Law.  This Note shall be governed by and construed in accordance
with the laws of the State of California.

         IN WITNESS WHEREOF, Borrower has executed and delivered this Note as of
the date first written above.



                                         By __________________________
                                                  Michael Radlovic


                                 Promissory Note

                                     5 of 5