I also purchased the combined operations from Steam yesterday.
the weekend special Arma 2 Combined operations.
Both games appeared to install OK.
BUT- When launching the 1st game, Arma 2, it gives an error message "bad serial number in setup" and just fails to start.
The 2nd game "Arma 2 Operation arrowhead" runs fine with no problems.
System - Windows 7 64bit ultimate OS
QUESTION - how do you run Steam "as administrator" in Windows 7 ?