Ok, story..Kinda OT..kinda.
I purchased a 2gb SD card for my mother's camera..and when I put it in there..it gave me all this error crap, not compatible..etc. So, I was sitting there..ub3r puzzled. I threw it in my laptop, and formatted with FAT and FAT32..That didn't help. Then I tried formatting it through the camera itself, didn't work. I made sure that the camera supported 2gb SD cards..It did..So, I basically forgot about it and left it to my mom..lol. Eventually, my mother took it back to BestBuy and the people there said "The card is too fast for your camera". I honestly had no idea that speed incompatibilities existed..so I basically learned something that day (assuming they were telling the truth).
In conclusion, perhaps your (generally speaking) cards are TOO fast for the Wii!?!? I'd highly doubt that...But, apparently it's a possibility. Perhaps, they're too slow? Ehh, idk.
Good Luck.