When running Export as Catalog on my laptop to transfer to my primary desktop editing environment I get a message that photo files are missing. They are there and visible in a file browser. I can export individual files with metadata and import but lose a lot of the work I had done on my laptop like pick flags and collections. Windows PC. I have this issue in both LR 5.7 and LR CC.
Photo files are missing usually implies that you have moved or renamed or deleted the photos (or the folders that contain them) outside of Lightroom. In particular, there may be an excalamation point icon on the photo indicating it is missing, or a question mark icon on a folder, indicating it is missing.
To fix the problem, you need to locate the photos in your operating system, and then follow these instructions to reconnect in Lightroom: Adobe Lightroom - Find moved or missing files and folders
Interestingly the photos are not marked as missing in LR while viewing in Grid or Loupe view. I have been able to isolate the issue to exporting directly to a USB 3.0 external drive. If I export locally and then copy to the hard drive it works fine. It even works if I export directly to a USB 2.0 hard drive. Must be a bug in the export program dealing with USB 3.0 device. At lest I have a workaround for now. Thanks for you reply.