Can't hear audio in multitrack session

I just finished production on a multitrack session. It was playing perfectly and all the sudden stopped letting me hear it. It's playing, but not audio is coming out of the speakers. When I open the session.mp3, it's just a blank line. 

I've opened the individual tracks as single wav's and they play and can be heard. I've opened a new multitrack session and the files play in there. Is there a fix, so I don't have to redo the entire production?