some photographs show as black placeholders in imovie 10.1
I make home movies with a combination of photographs and movie clips imported from Aperture. Never had a problem with earlier versions of imovie but I now find that some but not all of the photos show as black placeholders in the movie. My OS is El Capitan 10.11.1 I notice that this is a complaint in the Reviews of imovie 10.1 but see no solution or pattern. Suggestions?
Aperture 3, OS X El Capitan (10.11.1)