I don’t fucking know why I can’t eject USB hard drives. I installed the SysInternals apps, and best they can tell me is that Dropbox is fucking with the drives. I explicitly told Dropbox to not fuck with USB drives. I don’t know who’s lying, I just want whoever is fucking with the drives to stop fucking with the drives, OK??? OK.
OP has done the same. A file is in use/locked by an app even after the have issued an unmount/eject command. The file that’s in use may not survive.