Here's the basic procedure.
1. Delete all Splinter Cell Chaos Theory data/profiles/etc from the 360's HDD.
2. Insert the SCCT disc and let the system load an update. Power the unit off, then back on. (Power cycle)
3. Load SCCT, go to the versus menu and let it update. Power off/on again.
4. Load SCCT, go to the Co-op menu and let it update. Power cycle.
5. Load SCCT, go to Versus menu, Live and download the new levels. Power cycle.
6. Load SCCT, go to Co-op menu, Live and d/l the new levels. Power cycle.
7. Load SCCT and you should now be able to play all modes of the game. Just remember that CT's Coop mode will only work with 'same console' versions (360 w/360, Xbox1 w/Xbox1).
Official member of SCAA
(Splinter Cell Addicts Anonymous)