Lotus Notes: Resolve "Type mismatch" error

I recently had a user call inn to report that whenever she tried to delete an invitation to a meeting, she got this error:
 

 
The invitation in question would get an X beside it, and delete when she refreshed her screen.
The solution is luckily simpler than the error message could lead us to believe; a simple change to the preferences is all that is needed:
 

1. In the inbox, go to Tools, then Preferences
2. Go to the Calendar & To Do tab, then to Autoprocess
3. You’ll see that the option for Automatic Inbox Management is blank. Choosing any of the two options solves the problem,