Respectfully, Umberto, both posters have stated they have turned off their antivirus
That might not be enough. Some antivirus are so defective, that they still interfere even when turned off from their interface, and the only real solution is to stop their services, or uninstall them. I HAVE witnessed this first-hand on many user's system while doing live sessions to support them and yes, it happened several times. And, some users don't realize they have two antivirus running, like a real antivirus and an anti-spyware, and in this case they should be both disabled.
and the updater still cannot find the relevant file, even though it is present in the Addon Manager folder
That's precisely my point. Since the update cannot obviously fail to find a file in its own folder, the only possible explanation is some kind of external interference which, is usually an antivirus or a similar product.
Of course, if the updater was coded with the wrong file to look for, it would happen to EVERYBODY and, of course, it would have been fixed long ago...
To deny there is something wrong is ignoring what the posters and myself are reporting. So for the time being, I'm choosing not to run the Updater at all--the sceneries still seem to function anyway.
I'm not denying anything. There's surely something wrong, and it's in your configuration, either a software interfering, or some kind of strange issue with permissions, which might have gone corrupted in that folder.
Are you able to start the Couatl_updater2.exe manually ? Do you see errors ? If yes, which ones ?