maggots

Hi I just bought Combined Arms from steam. I installed both games ARMAII and ARMA2 OA. I played ARMAII fine and then I switched to OA and it wont start up it processes and even displays bohemia's signia then it crashes and says wrong serial number given at setup. I read a tread about this problem but it was ARMAII they were having trouble with. That thread was solved by 'running the game as Administrator'. What does that mean? I would really like to play this game but it can't even start. Please help.