I have had two lockups myself
Once Wallace was by the police station/newstand and he performed the action to look at the sign between the two and the game locked up, though the Xbox itself did not.
The other time was when Wallace used to the map. He was in the basement talking to that military guy (sorry, don't remember his name) and he used the map. The entire screen went black.
This makes me a little frightened to play the game as I don't want to lose progress.