Did you patch to recommended version. 1.15.10? Also, try moving the entire Stalker folder to (or whatever you letter is ) C:\, just C:\. so - C:\S.T.A.L.K.E.R Clear Sky Or... are you trying to run the game from the xrEngine.exe located in the Bin folder? If so, you need to use the shortcut that the game creates during installation of Clear Sky. I dont know what it is about stalker, but after a restart of my PC, i need to move the stalker folder to C:\ or ill get a crash, then after the next restart, i need to move it back to C:\Program Files (x86) and so on and so on. Weird.