Lightroom is deleting photos from my SanDisk card. I can insert the card in the computer, review the files in Windows, but when I open Lightroom, the images are visible for a few seconds, then they disappear followed by the dialog box saying no photos found. All the images are completely erased from the memory card. There are no files when I check with Explorer. This is a repeatable error. After losing a whole set of wildlife photos, I've repeated this several times at home, same result every time. Worked fine before this week. Lightroom 4.4, Windows 7. Help?