This week I noticed an issue with Communicator where all our users were getting an Exchange connection error:
Exchange connection error: 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.
This prevented out of office settings and free/busy presence from working. Later, I heard from some folks that they were not able to set their out of office message in Outlook 2007. When they clicked Tools/Out of Office Assistant they would receive:
Your Out of Office settings cannot be displayed, because the server is currently unavailable. Try again later.
Lastly, reports came in that clicking the scheduling assistant would crash Outlook. A few tests indicated that these Outlook issues were affecting all users. After checking all the standard Exchange Web Services items and finding no issue I came across KB 958934. It turns out that the recent server updates that had been applied installed .Net Framework 3.5 SP1, and that was the root of the problem. The actual fix is KB 952883, which unfortunately requires a call to MS Support.