Won't load on hard drive and can't do split screen

Other than a networking issue is your disc in good condition?

Do the multiplayer maps load up in Combat Training or split screen?

Have you tried installing your game to the hard drive?

Installing the game to the hard drive has solved this problem for me. I have yet to test it on Xbox Live, but loading a split screen and solo game has worked fine.

Do either the multiplayer maps or the zombie maps load when you try them in single player as in Split screen? If they do not load still then the issue is with your game disc. Is it dirty or scratched? Even DLC map packs will fail to load with a damaged
disc as vital game assets from the disc are still required for these maps to load too.

Things to try:

Cleaning your disc or taking it to a game store to have the scratches removed

Installing your game to the hard drive

Installing your friends or a rental copy to your hard drive and then using your disc to run the game.

I'm assuming split screen only based on that he called him his "guest". But I find it hard to believe they would remove split screen, unless its free for all, I'm pretty sure you can't split screen in that.

Does your console have a hard drive? If so, where did you get it from. Original Xbox games require an official Xbox hard drive to load. They won't work with the 4GB console on its own without a hard drive, they won't load from USB storage and they won't
work on cheap knock off hard drives from eBay either.