This is usually associated with your profiles, saves and/or downloaded updates.
There are two ways to fix this that I have heard of, both requiring that you delete ALL your Chaos Theory content from the Xbox memory (hard drive).
1. Delete all CT content from your unit. Make sure you are logged out of your Live profile. Insert or launch CT and get the first update, which will have you log in. Now go back to the dashboard and shut the console down, start up and again make sure you're logged out of Live. Start CT, go to the SvM (multi-player) menu and get prompted for that update, log in and download it. Back to the main menu, then the dashboard, shut down and back on. At this point you should be able to run SvM. If not:
2. Delete all of your CT stuff from the Xbox. Go to xbox.com and select the support link. Never mind, to complex, just click on
THIS link to get to the compatibility update page. Read how to download and create an update disc, do it and update your xbox using the disc. Now insert CT and everything should work, you may or may not get another update due to the NXE but if you do, follow the #1 instructions.