After serveral months of use, "Card Error" was shown on my Canon Digital Rebel for my 512MB Viking card, which was half full with pictures. Fortunately, I just lost a few of pictures. I tried to format the file; "Card Error" kept occuring on my Rebel. This 512MB Viking card is now used for my data files.Probably, 512MB Viking cards are not designed for high Mega Pixel camera and taking many shots in a short period of time (i.e. 3 shots/sec.). My Canon A40 has no problems when used with the 512MB Viking card so far. Probably, I am going to buy a 512MB card from Sandisk or Simple Tech.