I've just had another thought on your problem. Take a close look at the back of your card to see if the little gold panels are 'scratched' or marked in any way. I once had a 256mb Panasonic card which allowed me to use it two or three times and then wouldn't load properly. It either told me "the file you are trying to load is empty" or the red light that comes on when you actually load the SD Card itself, wouldn't go off but just kept flickering.

The answer was a faulty SD Card which was replaced by the retailer immediately as it was under 'lifetime guarantee'. No problem with the new one since.

Hope this helps.

Audrey