Darky Key Changer help

I used the Darky key changer and ban checker and it works. BUT it wont let me play. I keep getting the bad Serial number pop up whenever i join a server. Any ideas or help on how to fix this?

Go into your registry for bohemia interactive and arma 2 and delete arma 2 oa from both. Then go on steam and validate files for it and try again. Worked for me.

Make sure steam isn't auto updating your key, check your key after you join a game.