Why do you use ctrl+alt+delete for task switching? Try alt+tab.
Also when you have the menu open, alt+enter toggles windowed mode which is good for mission editing.
I can see why you find it useful to be able to do this.
I run Win 7 Ultimate x64 and can alt+ctrl+tab whenever I want and be back in game almost immediately I click on the arma.exe.
Sounds like the error might be something to do with how much memory the game is trying to reference. It's worth trying to solve, anyway.
Glad you managed to solve it!