Photos won't copy or delete
I have been transferring a lot of photos from iCloud Photos app into various folders (all backed up on iCloud). I have done this many times before to avoid having too many photos in the Photos app. Suddenly today I have been unable to copy photos from the app or from the other folders. 3 photos were on my desktop, and these won't go into the Bin and say I don't have permission, even though the information tags say I do have permission. I have tried force quitting all applications, switching off and restarting several times, but none of these work. Sometimes I get an error message -8400, but Googleing this doesn't come up with any answers. I've also repaired the Photos Library to no avail. Can anyone please help?
MacBook Pro Retina