I have an external hard drive and when I want to turn if shut it down while the computer is still running, I go to the bottom bar and click the green arrow that says Safely Remove hardware. When I left click it I get a Problem ejecting USB mass storage try again later.
How do I shut off the external hd without messing up any data?
Instead of trying to unmount the mass storage driver, try the actual drive. I believe if you double click the mass storage driver it will expand to show the drive.