1. Open your program menu and uninstall Battleye.
2. Open your Arma 2 download folder and delete the "Battleye" folder.
3. Verify Game Cache of both Arma 2 then OA
4. Open your steamapps>common>arma 2>BEsetup. and use the battleye installer.
5. Re-Launch Arma 2 then OA, it will fix itself and update Battleye by installing the most recent version.