"It doesn't appear you have Arma 2: Operation Arrowhead installed... would like to buy Arma 2:OA etc"
I manually put in all the directories and when I tried to update Day Z, it gave me a bad cd key error.
I have redone all the steps needed when you first start playing Day Z (start Arma 2 OA once with a certain launch options then start Arma 2 CO) but it still does not work help.