Working on an OCS migration project a few weeks ago I ran into everyone's favorite error:
There was a problem connecting to Microsoft Office Outlook. Your Outlook profile is not configured correctly. Contact your system administrator with the information.
After double checking the lengthy KB 2373585 article discussing Outlook/Communicator errors and ruling out the usual suspects I was stumped. After some digging around on the workstation I found the user had the Exchange 2003 System Manager and tools installed on the machine. Since the System Manager uses a slightly different version of MAPI components Communicator would generate this error immediately upon signing in.
The solution is to open a command prompt and just run the command: fixmapi.