Because of more comments asking for what a specific error code means, I decided to add a more detailed error message. It shows the text provided by Windows. Most of the error codes are usual code 5. In that case you most likely forgot to close the window, that got opened when you plugged in the USB flash drive. In that case the device can’t be locked and you can’t use Backup or Restore on this device. You have to close the opened window first.