Missing File message in Photos for Mac when copying referenced files
In Photos for Mac, I am copying referenced files (which are on my MacBook hard drive) into a Photos library. For some files, I'm receiving a Missing File message which states "Photos with unavailable original files cannot be opened. The original photo IMG_0271.JPG is either offline or cannot be found. Click 'Find Original' to reconnect." However when I click 'Find Original' and navigate to the file location, it is grayed out in Finder and cannot be selected. Any ideas why this is occurring? Thank you
MacBook Pro Retina