There are several possible fixes for this issue.

1) Running Steam application as Administrator:

  1. Exit Steam.
  2. Right-click on Steam icon.
  3. Left-click on "Run As Administrator".
  4. If the problem persists, reboot your computer and try the procedure again.

2) Delete registry entries:

  1. Exit Steam, open Start menu and type this directly into the menu (in Windows XP, you will have to click on "Run" first): regedit
  2. Press Enter.
  3. In regedit window, click on HKEY_LOCAL_MACHINE.
  4. Press CTRL+F to bring up search.
  5. Look for "ArmA 2 OA" (without the quotes).
  6. Delete all the "ArmA 2 OA" entries you find from the registry.
  7. Run Steam as Administrator.
  8. Right-click on the game in Steam Library.
  9. Click on "Properties".
  10. Select "Local files" tab and click on "Verify integrity of game cache files" button.
  11. Please wait, the process can take several minutes.

3) Reinstall Steam:

  1. Go to Steam's installation folder.
  2. Delete everything there except "steam.exe" and "steamapps" folder.
  3. 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.