Halo 3 won't let me play online??

[Danny W.]

I've had Xbox Live for almost 2 years. I never had a problem until a few months ago. When I try to play Matchmaker on Halo 3, every time I select a game type, it says "One or more players cannot play this match". It usually does it for guests of certain games, but I'm using the gamertag i've had for 2 years now. It never used to do this. The only match it let's me play is Social Slayer. nothing else.

any help????????

 

[Grimm]

there must be a new map pack that you don't have.