Having purchased Arma 2: Combined Operations on Steam today, I downloaded and installed Arma 2 and Operation Arrowhead. I then launched Operation Arrowhead, which worked fine, loaded up and played a little. I quit and then went to launch regular Arma 2, which went through the loading screens, got to the Bohemia Interactive screen and then shut down, popping up an error message reading "Bad serial number given by setup". ???
I then attempted to launch Operation Arrowhead as Combined Operations. This caused a DOS box to pop up, run through a lot of text, and within seconds it disappeared and then nothing happened.
Any ideas as to why? or how I can resolve these issues?