Why can't I delete files from disc on my MAC?

I can't actually delete photos from Lightroom on my Mac system. I simply get an OS message that says 'Unable to move file to trash can'. I know the difference between 'delete' and 'remove', have read many discussions threads on the topic of deleting photos and know to attempt the delete from the grid view in their original folder. ...I used to be able to do this but for some reason it no longer works. i'm quickly reaching my disc storage limit and have to get an answer soon.