I think what he's trying to say is...
When he first started to download the music store update he panic'd and thought it was a system update and probably unplugged his Wii during the update.
Now he can't do the update date again probably because it's corrupted. I don't know if this is a job for anytitledeleter or not. Somebody with more knowledge than I about the music store updating would have to say.
NOTE ********************
Never turn off in the middle of any kind of update like that. The harm you do will surely be far worse than that caused by the update itself in most cases.
It's pretty easy to downgrade from a system menu update so for the love of god and all that is holy ........... don't reset or power down during accidental update.