If you have Exchange System Manage installed on your client and are having issues with your Communicator client or Outlook integration, there is an issue with this configuration. There was a bug file on file for this issue but Exchange System Manager and Outlook is not supported on the same machine so the bug has been closed as won't fix.
One of the reason that the Addin is failing is because they use different version of Mapi32.dll files. Some customer have resolved there issue by renaming the mapi32.dll and doing a repair on Office, but this may cause you to have issue with Exchange System Manager.