What do i if in matchmaking in halo 3 it says one or more players doesn't have

[Brian]

the req. maps to play? Halo 3 - Big team Battle

 

[Triz]

if you have the map pack it tells you need then try another one then go back if it says non cold storage then you need all the other ones if you just have heroic pack look for ones that dont need a map pack or just the heroic pack