Bad serial number given in setup
There are several possible fixes for this issue.
1) Running Steam application as Administrator:
- Exit Steam.
 - Right-click on Steam icon.
 - Left-click on "Run As Administrator".
 - If the problem persists, reboot your computer and try the procedure again.
 
2) Delete registry entries:
- Exit Steam, open Start menu and type this directly into the menu (in Windows XP, you will have to click on "Run" first): regedit
 - Press Enter.
 - In regedit window, click on HKEY_LOCAL_MACHINE.
 - Press CTRL+F to bring up search.
 - Look for "ArmA 2 OA" (without the quotes).
 - Delete all the "ArmA 2 OA" entries you find from the registry.
 - Run Steam as Administrator.
 - Right-click on the game in Steam Library.
 - Click on "Properties".
 - Select "Local files" tab and click on "Verify integrity of game cache files" button.
 - Please wait, the process can take several minutes.
 
3) Reinstall Steam:
- Go to Steam's installation folder.
 - Delete everything there except "steam.exe" and "steamapps" folder.
 - Run "steam.exe" - Steam will reinstall itself automatically.
 
If none of these work, please send us an e-mail (you can use the contact form below) and we will look into your issue further.