I'm getting a no symbol (circle with a line through it) when I try to drag a clip to the timeline in a project. The clip will bounce back and not be added. When I try to use the "append to storyline" buttons, I hear the Apple error sound and the clip is not added. This only started happening once I updated to macOS Sierra. I have version 10.2.3 of Final Cut Pro X. Anyone have any idea how to fix this?