Ok well I found a few new things out.
First my clients mac is almost identical to mine and the project plays fine.
So he synced the audio somehow, using a plugin maybe? I am not sure about this.
When I drag the video files from the bin to the timeline they play fine, its just the existing clips that are in the timeline that don’t work. But if I drag the exact same clip in they work. I did have to reconnect all the media when I first got the project. Any other thoughts? Thanks!