The following reset procedure should work on these Brother printers - HL-L5100DN, HL-L5200DW, HL-L6200DW, HL-L6400DW
Open the front cover and leave open while completing the following steps.
1. Push both the SECURE and CANCEL buttons simultaneously.
2. Use the UP and DOWN arrow to select the type of toner you are installing.
3. Push OK to reset the selected toner cartridge.
4. When you see ACCEPTED on the display this indicates that it has been reset.
5. Close the front cover.