I had some issues with my Outlook 2003 Calendar at the office and had to create a new Calendar and remove the original one. I then discovered that the Reminders stopped working so this is what I did to correct that issue.

1. Archive the Calendar using today's data as the 'older than' criteria, using File->Archive
2. Shutown Outlook via File->Exit.
3. Run the following Commad via Start->Run. outlook /CleanReminders.
4. Shutown Outlook via File->Exit.
5. Run the following Commad via Start->Run. outlook /ResetFolders.
6. Done! The reminders sprung back to life.

Enjoy! I hope was helpful for someone out there!