I was certainly not trying to diagnose what the error message means. I can see what the error message implies, and what it implies is incorrect. So as far as that error message goes, the problem could be anything.
Getting a useless error message telling you to contact the administrator is even worse when you are the administrator.
But my main point is that a browser needs to give a meaningful error message regardless of the technical level of the user. Because a user who doesn’t have the technical knowledge themselves can still take a screenshot and send it to somebody who does.