I'm having an odd problem that I have no idea how to fix. Hopefully someone here can help

Anyways, I just got a 4 gig sdhc card and I put some music onto it with a card reader (i have a v1 e260) When I boot up the sansa with rockbox, it recognizes the card and the files but the files are corrupted or something. When I try to play them, it shows the length of the songs to be 0 and nothing happens. Any ideas and/or help? Thanks in advanced.
edit: I just tried copying some music through rockbox onto the card and it still doesnt play.... whats going on.... :/