2 possible options:
Option 1: If you are able to open Outlook, then go to the
Help menu and choose "Detect and Repair". If you cannot
open Outlook, then open another office program and
choose "Detect and Repair" from its help menu. (be
prepared with your original office CD). The Detect and
Repair repairs all installed office programs for that
version.
Option 2: Open Outlook in "Safe" mode (Outlook 2002 or
later only). To do this, hold down the Ctl key while
opening the program. This will disable any add-ins you
have loaded. Then you can troubleshoot if one of the add-
ins is giving you a problem by going to "Help --> About
Microsoft Outlook" and clicking on the Disabled Items.
Put the back one at a time. Close and restart the program
each time and see if you get the error. When (and if) you
get the error, repeat opening in safe mode and then leave
that add-in disabled.