Photos Referenced Files Not Accessible

While consolidating the files you could temporarily enable the option "ignore ownership on this volume". The "Ignore ownership on this volume" flag should be in the "Sharing & Permissions" section of the Info panel of the external drive. If the flag is missing, the file system may be wrong for photos.

Have you tested, if you can consolidate the files, if you just select one of the files? Do you get the same error message?

Can Photos reveal the referenced files in the Finder? Select one of your referenced photos in Photos, then use "File > Show Referenced file in Finder". Does Photos open the correct folder? Is the referenced file readable? Can you open it in Preview?

Are your referenced files on an external drive? Or where is the folder with the original files?

stevmeister wrote:

If I try to export the referenced files, Photos finds the fold but the file names are greyed out.

That is normal. The Export dialog will let you select a folder, but not a file. Otherwise the exported file would overwrite the existing file.

Where are your referenced files stored? Are they on an external drive? What is the file system of this drive? How is the drive connected?

Photos on High Sierra has problems to find photos or videos on an external drive, if the file system format is case-sensitive.

The File > Get Info panel for the external drive would be showing "MacOS Extended (Journaled, case-sensitive)", if the drive were case-sensitive. So that is alright.

Is the same drive used by Time Machine? Photos on High Sierra has problems, if the image files are on a Time Machine drive.

As a test, move a folder with some referenced files to your system drive and then try to consolidate the photos with "File > Consolidate", while the files are on your system drive. Does that work?

That did work, but I seemed to have lost face IDs on the newly imported photos.

Did you really import the photos? I meant, you should try to use "File > Consolidate ...". My hope has been, that you might be able to select the moved originals, if they are on your system drive, when Photos asks you to locate the referenced files.

Have to select the photos.

I thought you have an album with the thumbnails of your referenced files in Photos? Or is this longer the case?

. I have a smart album that shows all 12,000 referenced photos.

Did you already delete all of them ? Then the faces information will be lost. It is bound to the thumbnails of the versions in your library.

Window popped up asking for permission to access access my media file.

Where is this Media file located? In your user home folder on your Mac you should have the permissions.