Do you mean you can't use the back button? If that's so, then that's normal (I believe) because it's only stored your point up to where you are in the story. It won't let your go back, because it's only recorded where you are and the possible places you can go (again, I think so. I usually don't have to use the back button when I play saved games)
If you mean that you can't move forward in the game, then that's another reason that I do not know of. (your wording was a little weird so I'm not sure which you mean)
