Wrong CD key, Bad CD key, bla bla, every bug possible in the entire game

[Oerlinator 1]

Hello there guys! First of all I want to say, that I'm German and my English is horrible, sorry for that, the German forums are just too empty.

So, my problem is: I wanted to test DayZ on a friends Steam Account, he came to me, logged in, we installed ArmA 2: OA and ArmA 2: Free and the Six Uploader to play DayZ. Everything went awesome, except some shadow bugs where my shadows are sort of a grid of light und dark pixels. I played, had my fun, great mod. Immediately after playing 4 hours of DayZ, I logged into my Steam account and bought ArmA 2: OA and wanted to play on my account, everything went well, but I started on the same place where i stopped on my friend account. As he arrived at home and wanted to play with me, we noticed only one of us can play at a time. If I play DayZ and he wants to start it too, he gets the following information: "You are kicked from the server, Bad CD key". We had no idea how this could happen and how we solve this problem until we found this thread: http://dayzmod.com/forum/index.php?/topic/29424-error-fixes/ . I tried to solve the problem with this (but not my friend, maybe this is the problem? I don't know) and failed hen I needed to download the Beta files from the Arma site, because I have no normal ArmA 2. only OA and free. And now I am here without any idea of what to do, even if my friend doesn't play anymore I receive the message that the CD key is bad. I am sitting the whole sunny, wonderful day at home trying to solve this problem for like 12 hours now :( Can anyone help me please? I am also about to download the normal ArmA 2 on another friends account to get the beta patch going, will this work? I hope you can help guys.

[Oerlinator 1]

*bump* Is it possible that I need to change something in my registry? Or will it mess up things more?