Sometimes you'll run across this handy error message while trying to copy something to a drive. I have no idea what it means. But I do know that the Finder thinks the drive is still in use by something when in reality it's not.
- lsof | grep in the terminal reveals nothing.
- Using an app like WhatsOpen reveals nothing.
- Relaunching the Finder doesn't help.
- Repairing the drive with Disk Utility won't work because...
- You can't eject the drive.
You have two options in my experience.
A. Force Eject the drive.