Unable to eject USB Storage Device on Windows XP

Often you would see error message "The device ‘Generic volume’ cannot be stopped right now. Try stopping the device again later" when trying to do a safe removal of USB storage device, but you are pretty sure that no program is currently using it. That's because there are still open handles with certain files in the USB Storage Device are in use by some processes which cannot be seen at the built-in Windows Task Manager.

This Microsoft Support article explains the cause and offers the solution that requires a separate free utility, Process Explorer.