From here: Genius for iPod and iPhone
- "Genius is unavailable for the selected song."
If this happens, try making a Genius playlist with those songs on your computer. If you can make a Genius playlist in iTunes on your computer, then it is likely that there are not enough songs on your iPod or iPhone that go great with the desired songs. Try syncing more of your iTunes library with your device. If you are still unable to make Genius playlists from those songs, consider making Genius playlists in iTunes first, then syncing them to your iPod or iPhone.