iPod classic keeps ejecting itself from iTunes.

When I connect my iPod classic to iTunes it syncs and then immediately says ejecting and disconnects itself. I can still see the iPod in the "devices" pane of iTunes but can't access anything in my iPods library or add songs to it. Is there a solutionn for this? I took it to the Apple store a few days ago because it was resetting itself over and over and they re-installed the software and it seemed to work but now it's bugging out again.