Sparkfun MP3 shield with WAV

Does anyone have experience with the Sparkfun MP3 shield for Arduino? The software says it can play WAV, WMA and various other formats but I can only get MP3 to work. I suspect there is something missing from the libraries. I can get no help from the usual channels.

If you don't give a detailed description of the problem you're encountering you won't get any help here either.