Try this. Using a pencil eraser, rub it on the gold contacts on the memory stick as if you are erasing writing on paper. Do this for about 30 seconds or more until you get all the gold contacts. Put the stick in the camera, switch to 'Setup', then turn the camera on. The 'C:13:01' error will automatically disappear. At this point, quickly format the memory stick using the camera's format feature. CAUTION: NEVER FORMAT YOUR MEMORY STICK ON OTHER CAMERAS, USING A COMPUTER WITH A MEMORY STICK READER OR USING WINDOWS XP WITH A USB CABLE PLUGGED TO THE CAMERA. IT DOESN'T WORK. FORMAT YOUR MEMORY STICK USING THE CAMERA'S BUILT IN FUNCTION ONLY. Hope it works for you.
P.S. If this doesn't work, try the "Beat the crap out of it" technique. A few good bangs in the palm of your hand might cure it also.