I bought a retail version but my disc seems to be damaged (and it's gonna take loooong till I get a replacement), so I tried to install the game with a friend's retail and type in my serial. After the installation, the activator pops up and when I type the "install keycode", it says "Invalid Serial Number". Could it be that my friend's copy is from another country? I don't know if it is, it seems roughly the same edition to me, just asking. Please help with this cause I'm going nuts :S (and yes, I am reading the code correctly )