[Wall-E]

I'm not sure If you do notice this but try not format your memory cards in your desktop/mac but instead do it in your Dslr to format the card. I notice that most of my cards before where format using my desktop where get to be damaged in the long run. Either get corrupted or suddenly just drop out from detecting it.

The ONLY time you want to format a memory card in your computer, is iff you can't format it in your camera.

And, you want to format your card, rather than just delete the images. It refreshes the file allocation table, which can be corrupted by file deletions.

Wall-E