First, don’t panic! We’ll tell you why that happens and walk you through the steps to address it.
The missing file message shows up because Lightroom has lost track of the original image. You can see the image on your screen because the thumbnail preview still exists in the Catalog. The original, as we said, is gone. Without the original, high-resolution image, you can’t edit the image. (You can read more about rebuilding Lightroom previews.)
Lightroom will lose track of an image if it’s moved onto your computer. In other words, an image or batch of images was dragged out. When that happens, the program searches for it.