Thank you for your answer.
By testing all the mods I have in this game I discovered a very strange thing...
The "Gaus Sniper" Mod was crashing when I wanted to watch the USOpedia!
I discovered that now we shouldn't make any case errors with folder paths.
I had in the Ruleset: 0: Resources/
UFOPaedia/GAUSSSNIPERRIFLE.png
But the path was: Resources/
Ufopaedia/GAUSSSNIPERRIFLE.png
By fixing the case everything works!