I have 9,000 songs in my iTunes, and most of the ones I've tried work with Genius. Everything from obscure artists in weird genres to The Beatles and AC-DC. However, I've found that The Bee Gees, Creedence, and The Doors do not work. Also certain tracks from Prince ("When Doves Cry" does not work, but The Black Album works just fine). With one exception, all the tracks were pulled from CD's rather than purchased from iTunes (the exception being "Hey Tonight" from Creedence, purchased from iTunes but doesn't work). So bizarre! I know these songs work for other people, just not me!
Any thoughts on this? I note that these are all Warner Bros. disks, and most of them are from double disk collections. Make me wonder if there's a problem in the tags? The only one it wouldn't explain is the "Hey Tonight."
The song Sympathy for the Devil from Hot Rocks Disc 2 gave me the same problem even though genius was up to date. As an experiment, I changed the album to Beggars Banquet, which also has the same song, updated genius and taa daa, iTunes was able to generate a genius playlist.
Unfortunately, I can't tell you why the change worked.