How to clean up Outlook's Forms Cache

When you receive the message

The form required to view this message cannot be displayed. Contact your administrator

It usually means that you need to clean Outlook's forms cache.

To clear the forms cache in Outlook 2010 and newer, follow these steps:

1. Go to Filemenu, Options.
2. Click Advanced.
3. Click Custom Forms.
4. Click Manage Forms.
   
5. Click Clear Cache.
6. Restart Outlook.

To clear the forms cache in Outlook 2007 and older, follow these steps:

1. Go to Tools menu, Options.
2. Click the Other tab, and then Advanced Options.
3. Click Custom Forms.
4. Click Manage Forms.
   
5. Click Clear Cache.
6. Restart Outlook.

If that doesn't work, delete the Forms Cache Files.

1. Close Outlook.
2. Locate the Forms folder. In Windows 7, 8 or Vista, its at C:\Users\username\AppData\Local\Microsoft\FORMS
3. Delete all the frmcache.dat file and folders that are in the Forms folder. You'll have one folder for each custom form you have installed. If you haven't created custom forms, you won't have any folders here.
4. Re-open Outlook.

When you restart Outlook, and use a form Outlook will automatically reinstall the form, recreating the forms cache and index.

For a shortcut to the Forms folder, copy, then paste the following line in the address bar of Windows Explorer in Windows 7, 8, Vista:
%localappdata%\Microsoft\Forms

or in Windows XP:
%USERPROFILE%\Local Settings\Application Data\Microsoft\Forms