Whoa, slow down Tapeworm. Formatting is the nuclear option.
It probably is an unsupported file format–.m4a files from iTunes, perhaps. But it might also be finder files from albums ripped to mp3 by Apple computers. Connect the Fuze to the computer and Search it for MACOSX. You might find file folders under that name inside album folders. Inside the MACOSX folders are files with names like _01-Trackname1.mp3 that are 0kb in size. The Fuze tries to play them because they are called .mp3, but there’s nothing in them–they are just markers for Mac computers.
You can delete any MACOSX folders from the Fuze (though you might want to check in Properties to make sure they are 0kb).
And before formatting, you should also try mp3tag to fix tags. Follow these directions to fix a problem album.
http://forums.sandisk.com/t5/Fuze/Files-appear-on-computer-but-not-on-Fuze/m-p/248900#M49238
