Stuck in a loop
This problem first started with Chapter 1, Chamber 6 the coop game. We finish the chamber but the next chamber doesn't start. Instead, the last chamber repeats. This same problem has started with my individual game as well.
I am playing on Xbox 360. I was first playing off the disc. When the coop problem started I downloaded the IGN. No help. I loaded the program onto theXbox 360 console to see if that fixed it. No help. After I loaded the game I could not access the hub anymore so I downloaded IGN again. But still the hub option doesn't appear on the menu and the room still repeats.
How do I fix this.
I'm thinking somehow the transition script got screwed up and is doing this. Since you say it happens in single player as well it could be your disk... Does your partner report this problem when playing with other friends? If he doesn't, then I am 99% sure it's the disk and specifically the transitions manager.
I never have used an X-Box so I can't really say how to fix it, if it was on the PC I would say validate steam files though....
Maybe someone who knows more about X-Box consuls than me can help you out 
Good luck! And when in doubt, use steam support, they may know something about this.
I only use PC, but if there's a way to enable developer console (which there probably isn't), try that. If it works, enter the command:
map (levelname)
For coop, you both would have to be in the coop hub then issue the command.
Musical website Moddb
There isn't. And in co-op you'd need the "changelevel" command rather than "map".