Hey! If you are using GOG Galaxy, did you try to verify/repair the game? If not, go to the downloaded games in GOG Galaxy on the left side, right-click on the game's tittle, go to the 'manage installation' and 'Verify/Repair'.

You can also try to open the .exe file (as administrator) directly from the installation folder.

If it does not help, you can always contact our technical support here: http://bit.ly/GOGTechnical :)