Age of empires 3 Cd key error?

ok so the other day i whent out and bought age of empires 3 and i entered the cd key in and installed it then i played for like 15 hours on campaign and skirmish and i went 2 multiplayer and tryed 2 sign up and it says account error [100] cd key invaled or somthing like that and it says its a abd cd key and i cant find anywhere 2 enter it again and i went out and bought another copy and tryed it and it says the same thing every time i cant figure out wy it doesent work!