This is an issue that should have been resolved with some previous updates, most people do not enable updates for MS products (except Windows)
GI assume you are using XP, so go to http://update.microsoft.com and enable Microsoft updates, this will update Windows as well as MS office and will likely resolve your issue.
If not, back up your Outlook PST files and reinstall MS Office (File, Export, choose PST, and make sure you that everything is selected to be backed up/exported)
Astrophel
January 2009