when i click the shortcut to start the game the error message i get says cd or dvd is missing like as if its a game installed through a dvd ... but through gog its all digital nio dvd required or so i think .. whats the solution?

Try uninstalling and reinstalling from scratch. Install anywhere but under C:\Program Files or C:\Program Files (x86) because Windows always mess with stuff launched from there.

... and try running the game with administrator rights. Right-click the game's shortcut and select to run it as an administrator.

After playing this game for a few days without any problems, I suddenly get the same error message (No disk in drive). If i cancel this message twice the game starts without further issues. If any disk (does not matter which one) is inserted in my DVD-drive no error message appears. Game is not installed on my windows partition and i do start it as admin. Re-installing did not help.

Running Win 7 64bit btw.

Edit:
Last time I checked the error has disappeared without me doing anything about it. This is really strange...