The form you selected could not be displayed. Contact your administrator.

Description: User get error "The form you selected could not be displayed. Contact your administrator." or "The form required to view this message cannot be displayed. Contact your administrator." when trying to add something in the calendar.

Cause: Problem with the form cache

Solution: Rename the files frmcache.dat and usrclass.dat in users profile folder.

alternative solution:
1. Click Tools
2. Click Options
3. Click Other tab
4. Click Advanced
5. Click Custom forms
6. Click Manage forms
7. Click Clear cache

Doing this makes the following:
* Clears cached objects from the memory
* Deletes the frmcache.dat file
* Deletes subfolders containing previously cached forms
* Creates a new cache (for standard Outlook forms)