bkg73123, I have had many hours wasted with flash drives becoming invisable to my wii. It only goes wrong if i try to change the games. I formatted to NTFS and have not had problems since, My theory was data transfer rate problem, Drive got hot then PC threw up a write delayed error. I only use it for options testing 16gb cheap ebay I use 120 160 250 gb portable HDD mostly.
I'm no expert but It was an experience to share knowledge.