Outlook - Error Message FRMCACHE.DAT When Trying to Create or Reply to Email

Issue:

• Could not install the custom actions. The form cache file 'C:\Users\username\AppData\Local\Microsoft\FORMS\FRMCACHE.DAT' is not valid. Contact your administrator.
  
  

Resolution:

• Close Outlook
• Go to C:\Users\username\AppData\Local\Microsoft\FORMS
• Right-click on frmcache.dat and select Delete
• Open Outlook and test