Outlook calendar stops responding/freezes

[Jubee]

I have a user that is using Outlook 2003. Periodically throughout the day
(once or twice a day) when the user opens his calendar and tries to click on
anything, whether it be adding a new appointment, editing an existing
appointment on the calender, etc., the calendar appears to be frozen. I can
not open an appointment, can't click the new button, etc. If I goto the
inbox or contacts, everything works fine in there, it just appears to be the
calendar that freezes. I then have to close out of Outlook, end Outlook.exe
in task manager and re-open Outlook. Everything works fine then.

Any ideas?