Hi @SimoneMorgante, thanks for posting on the forum and welcome to the SimScale Community! 
Unfortunately, we can’t pinpoint where the problem is without taking a look at your project specifically. Could you please share the project URL? This guide explains how to do that in case you need it:
Also, when you see the generic “An error occurred” message, it’s likely a bug—or at least, the error message should be more informative. Please don’t delete this failed run, and as soon as you share the project link, I can report it to the team to investigate further.
Cheers,
Igor