Resolve "Can't right click on message in Outlook 2003" issue

For a long time, I haven't been able to right click on an email in Outlook 2003 (e.g. to flag it).  This is how to resolve it:

1) Exit Outlook and other Office apps

2) Go to C:\users\username\AppData\Local\Microsoft\FORMS

3) Delete the FRMCACHE.DAT file

4) Restart Outlook