I'm using LR5.7 on a Mac Mini running Mavericks and when I attempt to import a folder of new RAW photos from my external drive into my catalog instead of seeing a preview of each thumbnail photo I see the following message displayed: "Preview Unavailable for this file." If I highlight any other folder of photos the previews are all there. What is the likely reason for these previews being unavailable? JohnnyCam
What camera took these RAW photos?
Did you use any Nikon software to transfer the photos to your computer's hard disk?