Hi Tony I had this problem with the jolly to the folly movies and I found that youtube like to link each artist to your video so that the person viewing it knows the song name and the artist. There will also be a link under your video to purchase the song from itunes. Youtube gets confused when more than one song is used on one video so stick to one song per video.
Secondly don't use any recent songs as they won't have the copyright agreement in place. Instead go for an older song that fits.
I hope this helps, but it's pot luck as every song is different