Bad serial number given in setup

I can't launch DayZ because of this error. What do I do? I've followed these steps:
Step 1: Download the Key Changer program


Step 2:Go to Start>RUN Type "regedit" & click ok


Step 3: Find "HKEY_Local_Machine" Open it by clicking the little arrow and search for "wow6432node"


Step 4: Click on the little arrow to open "wow6432node" Scroll down to find "Bohemia Interactive Studio" and "Bohemia Interactive"


Step 5: Expand both Bohemia folders by clicking on the arrow, then delete both ArmA 2 OA's from them


Step 6: Open up steam, right click on ArmA 2 Operation Arrowhead>Properties>Local Files>Verify Integrity of game cache


Step 7: Once its finished, it'll say something like one file failed to validate which is normal so now launch ArmA 2 OA through steam and redownload the battle eye etc..

Step 8: Once your into the game menu of the ArmA 2 OA you opened through steam exit out and close steam



Step 9: Now with the CD key you bought paste it into the change key in the program darky key changer and change it

It works on my banned CD key but when I change to the new CD key it gives me the error message when I try to join a server. Help plz!

When did you start getting this error? And you normally launch with Steam?

A friend of mine had that randomly,too.
What he did is he uninstalled the game,cleaned registry with a registry cleaner,reinstalled the game.