I've had a look at the sesx and can't find any issues - in fact it 'plays' here but obviously without sound because I don't have the media.
I've sent you a slightly modified version of that sesx just for you to test - I'm not confident that it will do anything but it's worth a shot.
The only other thing I would suggest is to check your audio/hardware settings for the session and then maybe try moving some of the media to another location so that Audition can't find it - my thinking is that if it is not the audio/hardware setup it could be one of the media files - possibly the video.
So try moving the video file first so that it isn't present when you try to play the session.