I replied to an email and my reply appeared in the Sent list. It was still in "Local Draft" form because it hadn't actually gone yet. I clicked on it and hit the F key to forward it to a colleague and I got an error message stating the file didn't exist. That's fine but clicking OK didn't clear the message. I couldn't Quit either, I had to Force Quit.

No biggie, easy to avoid in future. Just letting you know.