Can't cancel a file transfer: keeps "preparing to move ..."

I did my usual transfer of files and decided to move a couple while the transfer was going on. Big mistake! Now, even though I’ve tried to stop it, I keep getting the cycling bar stating that it is “Preparing to Move to [file name]” and “stopping …” but not. I can’t trash or delete it.

Any thoughts?

You can shut down the computer and then it would be safe to eject out the drive without any issue.