new clip zip won't load music from mac

Songs are in music file.  clip zip is in msc mode (not auto).  It is fully charged.  It shows connected when connected to the mac.  sansa shows on the mac an we can move songs to the music folder.  The clip zip periodically says transferring.  but when left overnight to see if it was just needing time, when ejected, the clip zip remains EMPTY.  extremely frustrated

It looks like this is cause the files are coming down in a different file format.  Ones that are .mp3 are showing up. 

What is the format of the files that are not appearing–does the player support them?