[agracier]

I solved the problem! But is now possible to add a clean install? Not erasing my current one but adding a cristal clean install

Do you have an extra hard disk? Or an external hard disk?

If so, then copy your working directory of the game to that external hard disk, and keep it safe while you un-install and then re-install the game.
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Or else follow the procedure above with renaming the game with an '_' and then reinstalling.
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Once you get it all fixed up, remember to always, always, always keep a clean, freshly installed copy of Sturmovik in a safe place.

You can upgrade a copy to versions 4.08/4.09 and then mod to your hearts content.

But always keep a clean copy saved away for emergencies ...