[Guest]

Yes, difficult to track down such errors. Only suggestion is to get a new SD card and retire the old one. I think that a card failure is more likely than a camera failure, from what I have seen in the past. Flash memory does go bad with time, as it (or rather, individual storage units on the chip) has a limited number of times it can be erased and written two. Of course everybody says it won't happen in your lifetime....  I tend to not erase individual images, but let the chip fill up, and only format when almost full to reduce "wear and tear". 

Contacts can go bad as well. (moving it a couple of times in and out ("scratching") can help there). You could also transfer images with the cable from the camera, reducing the number of times you put chip in/out - helping to prolong the life of contacts.