Same happened to me and my camera.
-What I did was put my Wii's "private" folder onto a different SD card by saving some data on it (i.e. Smash Bros Replay data)
-Load the whole folder onto the computer. Then put that folder onto the "unreadable" SD card and it started working for me again.
What you need is:
-2 Different SD cards (any size [not sure about 4+]; reccommended 1 or 2 gigs) on FAT 32
-SD adapter with SD reader
Not 100% sure it'll work