Could be moisture build up on the memory card contacts. Have you touched the contacts with your fingers at all? Try using a clean soft eraser (such as a pencil eraser) on the contacts by rubbing gently and using a clean lens cloth to wipe the contacts clean. Don't use an abrasive or dirty eraser as that could scratch the contacts. There are also products that you can buy to clean the contacts as well.
Have you tried a different memory card? Sometimes memory cards fail, so this would determine if it's the memory card at fault. It is possible that only a portion of the card went bad, so you could try to format the card, but be forewarned that you will lose anything that is on the card once you format it. I would just try using a new memory card first. If the new memory card does the same thing, there is a possibiity that some of the contacts may have gotten bent out of shape and are not making the proper contact with the card. Examine the contacts to see if there are any that look misaligned.
Unlikely, but it could be the circuit that reads the card that is to blame. That would require a visit to the repair shop, which gets expensive.
Steve M.
