Music file is not well formed.

I keep getting this error when trying to add music to a slideshow in LR. I've spent the entire day on the phone with both Adobe and Apple tech support.

I've installed other versions of LR, reinstalled this version, tried other music files, tried a new catalog, restarted computer in safe mode, restarted and only ran LR with no other apps running, removed all LR preferences, etc. Every thing the tech support suggested, I tried. We finally found that if I created a new user profile for my iMac and logged in as that user, the music in the slideshow worked. Adobe says this indicates the problem is related to the Mac user profile.

Called Apple and they said it might be related to the user profile, but there is no way they (apple) will know where all of the user preferences for LR are kept, and that I need to talk to Adobe to get it fixed.

I've already had to try a workaround for 5 client ordering sessions and lost two days' work. Someone please help!