error code 103

my friend quit playing this game so i borrowed it from him and when i tried to enter the cd-key it keeps saying error code 103 cd-key is in uses so i told him to uninstall it and this message still keeps coming up can any of you help me

CD-keys cannot be reused - if you want to play with your friend's copy, you will have to play it with his account email/password.

just download the client from the site or install the game , im not sure but i think you don't have to put in the key, it just asks you that if your trying to make a new account.

So just instal the game ( either from cd or download from site) and enter your buddies login and password and you should be playing.