SBS license problem

Please be more specific.  Are the client PCs receiving an error message when they attempt to login?  Are they all part of the domain?  Can they ping the server?

yes they can ping the server fine, plus they can login all that seems affected is exchange ?

OK, what is the problem that you're having with Exchange?  Are you able to setup their email accounts in Outlook or are they not able to do a send/receive?

basically when i setup the MAPI profile it sees the server fine, but when i close the wizard and open outlook it is giving a standard can not connect to the server.  The following is logged in the server event log.

Event Type:      Error
Event Source:      MSExchangeIS
Event Category:      General
Event ID:      9646
Date:            23/07/2007
Time:            15:38:01
User:            N/A
Computer:      ALCOHOLSBS01
Description:
Mapi session "/o=ALCOHOLSLTD/ou=first administrative group/cn=Recipients/cn=Adam.Wallis" exceeded the maximum of 32 objects of type "session".

 For more information, click http://www.microsoft.com/contentredirect.asp.

Install Exchange SP2 if you have not already done so.  Next here is a Microsoft KB article regarding your problem.  It should help you out
http://support.microsoft.com/kb/842022

exchange sp2 is installed, i am sure this has something to do with the server

installed licenses : 25
maximum usage : 10

why is the maxium only 10, when we have added 25 ?
 what do you think

This has nothing to do with your licensing - there's something else at work here you need to resolve.  You'll do this faster if you stop trying to convince yourself it's licensing related.

I would suggest you review the links provided by bluetab and then also look up the event ID at www.eventid.net - a subscription to the site is cheap and it can be very useful to have to help resolve your various event log errors and warnings over time.

Check out:
www.eventid.net/display.asp?eventid=9646&eventno=3449&source=MSExchangeIS&phase=1