I've done the above methods as well to no avail. Not sure whats going on. Also, my friends say that i am getting the "signature check timed out" error.
Uhhhh, as long as he has a steam account he will have the game. Of course, wherever he was he would also have to make sure he had the latest DayZ files as well. Also, he would have to re-download the game on the other computer. Is this trolling?