try to follow Oberguru's advice:
http://wl500g.info/showthread.php?t=...highlight=vfat
which is:
1) dd if=/dev/zero of=/dev/discs/disc0/disc count=1
2) repartition + reformat
P.S. I have a strong feeling that dd if=/dev/zero of=/dev/discs/disc0/disc count=1024 could be more appropriate