I have this problem with my canon A620 camera and am posting to this forum for possible solutions.
1) I have had this camera for about 15 months and use a Kingston and a Sandisk SD cards on it.
2) About a week back the camera started complaining of the "card locked". I checked the SD cards (both Sandisk and Kingston) and they are NOT physically locked.
3) When I put the default cards supplied by Canon ( the 16 MB ones which do not have a physical lock on them) in my Canon A620, the camera is able to shoot pictures.
4) I put these cards on my Canon camcoder and the cards are write able, no issues here.
5) I tried this too --> I formated the card on the computer, the card was formatted. When I moved it to the camera, the SD card is still not write able, so the formating option on the camera is greyed out (non functional).
I appreciate all your help.