The router's MAC address can be found on a label on the circuit board.
This is the location of the jumper pins that need to be connected (with a jumper). The pair of pins is located towards the centre of the circuit board.
The pair of pins are positioned next to a rectangular metal block (which is a clock crystal).
The jumper needs to be placed on the pins like so.
Once the rm_usb.bat file has started, this message should appear on the screen.
If you don't plug the USB cable into the PC's on-board USB port (e.g. if you use a hub) you will see the following error message.
You should be prompted for the router's MAC address during the flash.
Enter the address from the label first, then enter 00-09-F3-FF-FF-FF.
During the flash process you should see the above on the screen.