Can you include a little more detail?
Are you playing single player or multiplayer co-op?
Have you updated recently?

Try clearing your cache, maybe that will help.
More details would be helpful.

If you have Halo 3 ODST and u see the halo 3 M.P. disc in it then you have the Halo 3 Mythic map pack and Halo 3 M.M.P. and u need to buy the regular Halo 3

I would think there may be a scratch on it towards the middle of the disc.

if you purchased halo 3:ODST a secondary disk should be in the case if you bought it brand new. it says the name is halo 3 indeed but if you look under that it says multiplayer that means the campaign is not provided. if you havethe true halo 3 try unpluging your xboxlive cord/network adapter or simply wipe the disk down

extra:if you purchased ODST dont buy any map packs for the secondary disk all the maps are already loaded into it

your welcome for the info

if you purchased halo 3:ODST a secondary disk should be in the case if you bought it brand new. it says the name is halo 3 indeed but if you look under that it says multiplayer that means the campaign is not provided. if you havethe true halo 3 try unpluging your xboxlive cord/network adapter or simply wipe the disk down

extra:if you purchased ODST dont buy any map packs for the secondary disk all the maps are already loaded into it

your welcome for the info