Hi
I'm guessing that this isn't the hard drive that has Windows on it?
Courier is a standard Windows Font, your computer probably thinks it's in use though that seems odd since it's already in the Recycle Bin on another drive.
If you have Malwarebytes installed go to the More Tools tab and try using File Assassin.
Or boot into safe mode and try from there.
I've had folders that just wouldn't delete, until I turned off the UAC.
Mike