Originally posted by dShelly I don't know how else to explain it, but when that happens the photos disappear from the memory card and I have to format the card in order to reuse it. Has only happened once. I hope it doesn't happen again.
Even if the card shows up empty when you open it up on your computer, it doesn't always mean that anything is lost, you can use a data recovery application to dump all the raw data off the card if it comes to that. When a memory device gets corrupted, often times the list of files that's on the card gets lost and not the files themselves.
Memory and storage devices really don't like rewriting data unless they absolutely have to, so more often than not when you delete data all the system does is "mark" the files as though they're not there anymore, but won't actually overwrite the data until all the data has been filled up and it loops back to the beginning.
For instance, on a 32GB SD card I get 500+ shots with the Z, this means that I have to shoot through over 500 images before the camera overwrites the first photo that I deleted, no matter how many times I erase or format the card.