Try to copy all your files from your sd card and put paste it wherever you want to put it.
(NOTE COPYING THIS FILES WILL TAKE A LONG TIME)
Then format your SD card
If that didn't work just try the Gecko OS Channel
First Download this.
Pimp My WII
http://www.mediafire.com/?6fk8mo30acmhv7sGecko OS channel for wii
http://www.mediafire.com/?0o3wrzjjnmz(Just put this on the root of your SD card)
1:Open up Pimp My Wii on homebrew hannel
2:After that Select Wad
3:It will say found (Number) title
4:Then there's the screen where it will tell you to press B
5:Then after that it will tell you to select a source device pick "Wii SD Slot"
6:Look for the file where you put the Gecko OS Channel for Wii file
The one i told you to put on the root of the SD card.
7.Then wait for it to install the WAD
8:Go back to Wii menu after it's done installing
9: Then you will see the Gecko OS channel.
10.Pick the Gecko channel and it should work fine