each slideshow has one song associated with it
Were these songs purchased from iTunes? If so, you should take these preliminary steps.
1. Burn the music in question to a CD.
2. Reimport the music as an AIFF file. iTunes>Preferences>Advanced>Importing>Import using: (drop down menu) AIFF encoder
3. This music can now be imported into your project.
You might be dealing with more than one issue. If you do have iTunes music, follow the above procedure and see if the problem is resolved.
I hope this helps.