Still having some problems with this. I've tried updating all of my drivers - all of which are up to date. Day Z Commander won't even launch the game, it just hangs - Play WithSIX will launch it, but upon logging into the server it'll get stuck and after CTRL-ALT-DEL to desktop I see it's thrown up the Semaphore error. I've updated all drivers, uninstalled .net 4 and installed .net 4.5, I've run Chkdsk and it's all coming back clear... Steam can play both Arma games without error, it's only affecting DAY Z. (Verifying the integrity is fine also)