Need for Speed: Most wanted.

 Can anyone help. My two sons have an Xbox360 each and both have individual  need for speed most wanted  games [one disc for each xbox].

     My eldest sons game is logged into his xbox with his profile through this autolog thingy, but he also logged into my youngest sons xbox with his own profile aswell when they were playing together.

  Since then when my youngest son goes to play the need for speed most wanted on his own xbox360 he cannot go online with it because the autolog comes up saying that a profile is already with this xbox and can`t log in using his own profile?

  I am assuming that this is because my eldest logged into my yougest sons xbox360 beforemy youngest son had chance to log into it with his own profile..

       How can i get round this as i have tried to delete and reinstall need for speed but still won`t log in with my youngest sons profile??