I followed the instructions from http://support.apple.com/kb/HT1449 on how to move my iTunes folder to an external hard drive. After the move was complete I was able to play all my iTunes content through iTunes on my iMac and through my Apple TV that is sync'd to it. The problem is that any new items I have downloaded since the change will not sync with Apple TV even though I can watch them on iTunes without any problems.
I have restarted everything many times and sync'd & un sync'd Apple TV but nothing seems to work.
I am at a loss for what to do next, any suggestions?
It seems that while changing the file location of my iTunes library I also changed the iTunes store HD download setting from 720p to 1080p. As I have a 1st generation Apple TV it cannot play the 1080p content.
I changed the setting back to 720p and downloaded that version of the file from iTunes store and all seems to be working again.