Do you have an image in the folder containing your music files.
See here
http://community.wdc.com/t5/General-Discussions/Playing-all-files-in-a-folder-of-MP3s-repeating-first-track-then/m-p/95972
and here
http://community.wdc.com/t5/Firmware/Bug-Music-sequence-quot-Normal-quot-behaves-like-quot-Repeat-All/m-p/68354