@naytchSG: Sorry I forgot to mention in the original post that I already did that at that time.
@Derek Paxton: This fixed the problem partially. After deleting this folder it crashed directly after launching the game. I tried that a couple of times and in combination with deleting the MyGames folder I was able to reach the main menu. "Problem solved" I thought but a new problem arose: every 3D content was just white/shades of grey
Menu items and HUDs where visible but things like the sovereign in the sovereign selection window or the tactical map in the game were invisible. Zooming out to the cloth map worked though.
I remembered reading about something like this. Hence, I played around with the antialiasing settings (in-game, config file and global config). Somehow the problem got solved but its root still remains unclear to me. Suddently everything was back to normal although I'm using the previously set settings. Antialiasing works too. I never had these problem in WOM, previous betas or any other game.
