Why can't you sign in a guest account on halo reach?

@"you actually can if you have 2 controllers and your on split screen or multiplayer screen on the game you should be able to press the A button and you can sign in from there"

Logically you would think that, however when my live enabled account is signed in at matchmaking and i try to sign in a second player as a guest it immediately logs all players out and says "You must have an xbox live enabled account"........Help?