Originally Posted by
Plutonsvea
Ahh, that's your problem right there. Once you change your key, you can't start Arma 2 OA through steam because it resets it again.
Try going to the following:
64Bit: C:\Program Files (x86)\Steam\SteamApps\common\arma 2 operation arrowhead
32Bit: C:\Program Files\Steam\SteamApps\common\arma 2 operation arrowhead
Or wherever you installed your Arma2 OA
Launch Arma2 from there, and you're good to go.
And don't worry. You can still use DayZ Commander, just go to settings and untick 'run through steam'.