...to reinstall WOFF would be? Sadly, I have a "simulation.xml" error message when I start WOFF, I can´t start the simulation anymore. Should I completely uninstall the whole sim and its modules, and reistall from zero or may I try to repair it by running the main WOFF installer?

The correct deinstallation and installation ways are to be found in the FAQs on the OBD Website.
I can only recommend to check them out:

Wings Over Flanders Fields - FAQs

That's an odd error to get...

By the way, AV stopped, exe run as admin, but same error.

Aris, try the "Repair" function in "Workshop", before you reinstall.
You will loose all your pilots, but you would anyway. It's worth a try.

Install the latest update again - it will put a fresh one there. Check your file is not set to read only. Maybe if you use mods check.

Hard to believe but reinstalling the patch fixed the problem!!! Thanks Olham and Pol, I am very grateful to you! Next round is on me!

Well, it was rather Pol alone - he gave the correct advice.
But I'll have the pint anyway, if I may!