Are you talking about a game, or what? If it's a game, then you're pretty much screwed. Corrupted data can't be recovered. This happens when you are in the middle of saving, and turn off the console. I hate it when this happens. What game was it?:mad2:
It has happened to me, but not to anyone else I know that has a Wii. Knock on wood it hasn't happened to me in a while. I never figured out how to fix it or tried to fix it though.