reference from-
http://social.technet.microsoft.com/Forums/en-US/outlook/thread/5038892c-7a2f-411c-a4e4-9e2c148a628f
Can you check if the behavior changes if you start Outlook in safe mode?
- Quit Outlook (and Office Communicator)
- Through Task Manager, make sure Outlook.exe (and Communicator.exe) is not running.
- Start Outlook while holding the CTRL key down.
You could also create a new Outlook profile and see if it helps.