Yeah, my parameters were "-winxp -maxMem=2048 -maxVram=2048 -nosplash -noPause -cpuCount=4 -exThreads=7". Seems like after deleting "-winxp" the game wont crash when in menu and Alt-Tabbing. Have to try ingame when servers are up again.
Thank you for the solution.

The error happens randomly ingame. Doesnt matter how long you play it just crashes after like 5-10 min. Shadowplay is enabled. My Rig can handle the game. GPU: GTX 670 CPU:i7-3770, 8gb ram. Resolution 1920x1080. In Experimental, didnt test in stable. Server was around 40-45 players.