Four players in local lan (Age of Empires II - Conquerors exp)

i want to have four players when playing multiplayer age of empires II the conquerors expansion. It works fine when there are three of us, but soon as we add a fourth player, it says insert CD? THe host machine already has a cd, so we copied it and put one in the 4th machine, but it still doesnt work. Doesnt the game allow more than 3 players to play???
Pleassssse help
Thx :)