Outlook 2007 installed on Win XP SP2

My installation is not on a network and I don't share calendars or publish
them to the web (or anywhere else for that matter). I enter my appointments
by typing directly into the day view of the calendar. I do not enter by
bringing up the new appointment dialogue.

Randomly, a Save As window pops up and the program freezes, sometimes for
hours, other times I give up after leaving it overnight. The program is
trying to get me to save the calendar as an iCal (*.ics) file.

I have already disabled all plugins except my antivirus plugin (Kaspersky)
and Microsoft VBA for Outlook.

Can anybody help me get rid of this annoying problem?

TIA

Roberta