I recently upgraded to Mathematica 12.1. I have received the error shown in the following graphics.
Second image after clicking "OK".
I have received advice from Technical support and reconfigured locations. The error persists.
The other functionality of Mathematica appears intact and there are no issues with any other programs on my machine.
I have uninstalled and reinstalled to no avail.
I would be grateful for any advice.
This problem has been fixed by a paclet update, which can be installed by evaluating
PacletSiteUpdate /@ PacletSites;
and restarting Mathematica.
More details about the underlying cause of the bug can be found at
Thank you this resolved this issue.