You have OCS 2007 R1 deployed in your environment and began noticing MOC (Microsoft Office Communicator) clients display a notification:
Exchange Connection Error
… with the error message:
Communicator could not retrieve calendar or Out of Office information from Exchange Web Services. Communicator will automatically continue to retry. If this problem persists, contact your system administrator.
While there are various reasons why you may see this message and the first item to check would be your Exchange Server 2007 or 2010’s EWS services, if you determine that the service is configured and in working order, check that your MOC R1 clients are fully up-to-date. Microsoft has acknowledged that this can be caused by an earlier version of MOC and patching the client may solve this issue. The patches can be found here:
More information about the root cause can be found in the KB articles listed above.