Compatibility problem LAN

Hi. I have this problem : i want to play CoW on LAN with my friend but i get 'game incompatibile' message when i try to join his game and vice versa. It wouldn't be strange if not the fact that his CoW is actually COPIED from my HDD and is EXACTLY AND TOTALY the same. Any suggestions how to solve it?

Do you both have the same version of Kingdoms?

Also, did you or your friend change ANYTHING after the transfer process?

Maybe you uploaded to a new CoW patch? Also try Hamachi.