My iPhoto slideshow doesn’t play music from iTunes
If you have created a slideshow in iPhoto and attached music from iTunes to a specific slide or the entire slideshow, there is sometimes a step you have to take in iMovie for the music to play.
Open iTunes and select File --> Library --> Organize Library from the menubar.
Check the Reorganize checkbox (DO NOT check the Consolidate checkbox).
Go back to the iPhoto Slideshow, select the Music in iTunes again and it will play.