Lightroom 5.7 on my Macbook Pro OSX 10.9.5 will sometimes lose a photo while it's being edited. Suddenly there is a 'this file could not be found" message, the edit history goes dark, but the photo is still there, albeit no longer able to be developed further or exported. Back in the library module, the histogram is blank, and there is no exclamation point in the grid photo. Nothing happens with the search for the lost photo. Any ideas? I posted this issue about 10 days ago and I received an email requesting screen shots, which I sent, but I've since heard nothing back.