I'm using SanDisc as well with no problems.
I take it you tried playing back the audio files directly from the SD through your PC once you copied the songs/audio across?
The mp3 player in SW is optimised for 128kbps playback so anything fancier may not work. Other audio formats probably won't work either.
Could it be a LINUX problem. LINUX tends not to support USB devices as easily as Mac/PC.