iMovie not playing Apple Music Songs - protected and unavailable

I am running El Capitan and iMovie 10.1.1. I cannot see any of the music I have downloaded into a playlist which I believe are since I've signed up to Apple Music. Other songs which I had as part of my library from before I signed up to Apple Music are there. iMovie states 57 files are protected and unavailable. How can I get those songs into iMovie please?

Thanks