I know that this issue is probably due in part to the fact that those game modes are not fully reliable yet, but I think it's worth reporting since it seems that most of the other players don't experience so much CTD.
As previously said, I tried with the dev version. I also tried beta drivers for my GPU, running as administrator, reinstalling the game, adding various launch options, uninstalling my antivirus, removing profile files, turning off all the other programs, but nothing works...
I attach the Dxdiag file and you can find my arma 3 Alpha folder at this link:
http://rapidshare.com/files/3347239137/Arma%203%20Alpha.rar