I'm experience this issue as well. I was using my first gen Zune with about 15gb of music on it and it was working great. Then out of nowhere it just hangs on a song. Nothing would get the music playing again - I tried disconnecting the Zune and reconnecting it and shutting the car down to no avail. Sync eventually crashed and rebooted and when it came back it played the Zune for a while but ultimately froze again. I've replaced the Zune with a USB HD for now.