Photos says "These items cannot be added to your Photo library because the file format is not supported by Photos."
When I try to access my photo library via Photos I get the message "These items cannot be added to your Photo library because the file format is not supported by Photos.". When I click OK I get a very small selection of photos displayed, presumably from an older photo library? The photo library is stored on an external hard drive. I also migrated an older library to it some years when I got my current MacBook Pro. I last viewed my photo library a few weeks ago, and it was all there, don't know what's changed.
Running 10.14.4. Photos 4.0
Any help?
MacBook Pro 13", macOS 10.14