Back again. Reformatting made no difference, and it looks like others are having the same problem as me. I'll post my specs in case there's an off-chance that something's wrong:
Wii: Ver. 4.2U (Got it X-mas 2006, so it's far from new)
IOS: 58 (rev 6175)
USB: Western Digital 250GB (Fat32, 32kb...