iphoto lost my original files
I have several folders in iPhoto, the one in question, I have opened several times, and have edited some photos. For reason unknown, I tried to open, and enlarge a photo to full screen image to view it, and I suddenly could not. I got a warning that iPhoto could not locate the original file. I neither deleted or anything else with these files other than some editing, they are recent pics.I can still share the pics in iPhoto, but can no longer open the files to full image to view. My concern is that iPhoto lost my originals, and it could happen to my other folders. I did backup my photos, but when I redownload to iPhoto, I get the same warning of "original files lost"? What can I do to fing the originals on my MAC book, and how to prevent in the future?
MacBook Pro, Mac OS X (10.7.5)