iMovie 10.1.15 photos previously used won't drag to work area
Trying to create a movie in iMovie 10.1.15 with an mp3 as the sound track and photos as the base for the video. Done it many times before using photos in my favorites album in Photos. Now photos that I could previously drag to the workspace will no longer drag to the and load in the workspace. Other photos in the same album will drag. I can tell no significant difference in the files, some jpgs work and some won't, same HEIC, etc. The ones that won't drop in will show the outline as I drag them down but there is the mouse pointer head with a circle a a line through it and then won't release in the workspace. All photos have been used in previous iMovies with no issues.
Any ideas on why the photos I previously used won't work now?