UPDATE: Making a setting change didn’t clear the problem so I downloaded and activated Tweak Options.
When I tried to delete wppa_cached_options it asked if i was sure, I said ok, I got the same error message as before, to which my only option was click ok.
I then tried to delete wppa_cached_options_admin and the same thing happened, but it actually deleted this one.
I then tried to go back and delete wppa_cached_options, got the same error message, and the file remains in the list, undeleted.
The error message remains.
Thanks for your help.