Ah, the bane of my existence. What kind of device are you using? The problem is the copyrighted music, which the music companies (not YouTube itself) restrict on "mobile devices" like iPhones, Droids, and iPads.
The strange thing is that for a while they tried to restrict it all together. There was a huge outcry from the public simply trying to post a video with no profit motive in mind. Hopefully, they'll relent on this in the future.
This is the reason I've posted all my videos at vimeo.com/brutewolf. Vimeo also has a mobile app which allows the videos to play fine.
If you're not on a mobile device, then I don't know.