I spent the last day fixing a problem I had created for myself. I saw a few posts going around and thought this will definitely help someone. Windows 7 64 Bit Service Pack 1 - via Windows Update After I installed this, Arma 2 or any of the other expansions / mods etc stopped working. It took me a while to figure out, as I had made quite a few changes to my os and I finally narrowed it down to this. The app would launch via steam, all the boxes tick except for last two and then it crashes with no error report. No error is reported in the arma2 error log file either. Although this is a known issue with steam and service pack 1, there is not much mention of it anywhere else in relation to ARMA2 or DAYZ. Most related posts are answered with open as administrator etc etc... this doesn't help. So if this has happened to you, then you need to either uninstall the service pack or reinstall windows 7 and not update to it. After doing this, I had to mess around a bit to get Dayz working again. Most importantly is to install the beta patch, copy the new .exe over the original and change the command line in launch options for ARMA 2 OA in steam. I hope this helps someone out there....