Apparently, some Assassins Creed 2 players are reporting a glitch that traps the player in the Hideout with no way out of it.
The error occurs when players save and shut the console down after finishing Chapter 11. Upon restarting, the only way to escape the Hideout is to begin the game anew.
CVG has contacted Ubisoft, and until a response is issued, the site recommends you not "quit out of the game".
Just go play something else until a fix or workaround is announced, we reckon.
More through the link.