Never found a solution. Took both camera and memory stick to an autherised Sony repair workshop who tested both and confirmed no problems with the camera, but the memory stick had been subject to water and was corroded. Very strange beacuse it is either always in the camera or in the computer when transfering images. Purchased a new memory stick and have had no further problems. Can get a good buy on memory sticks on e-bay. Found Oz-auction at ozauction@gmail.com to be very ethical and provided great service. Good luck with it. nick