When a user starts Outlook 2003 from within Citrix, they receive the error:
SBCMSYNC.DLL is not a valid Office Addin
How is this resolved?
http://support.microsoft.com/kb/235009 looks like the solution to your problem, though oddly I only see this fault referenced for users of 2000 or 2002.
Have you installed 2000 before then upgraded to 2003?
Either way, if you have 2000 disk #2 with you, try inserting that and running through its 'repair' or 'maintenance' install.