UGH, i'm having the same problem with my 8gb sdhc.
I just bought the powershot sx120is about a month ago with a centron sdhc class 4 8.0 gb memory stick. after about 300 pictures, the card formated itself, i didnt know what the problem was till after about 200 pictures later, the camera started reading memory card error, card locked! i don't want to loose these pictures and i know it isnt a problem with the camera, my other memory sticks work just fine on it. it isnt the little lock slide on the side problem either. and it can't be because it's dirty or anything. is there a way to fix it. i'm going a little crazy here