Flashing firmware manually is a high-risk procedure. You should never unplug the USB cable or the power cord during the process, as this can permanently damage the main PCB (circuit board) of the printer.
The most frequent reason is the replacement of a printer's main PCB. If the main circuit board of your Brother printer is replaced, the new board often comes without any firmware installed. To make the printer operational again, a service technician must use filedg32.exe to transfer the necessary firmware files onto the new board. Service manuals explicitly guide technicians through this process: brother filedg32.exe
The binary file is mismatched, corrupted, or the printer did not fully latch into its structural bootloader state. Flashing firmware manually is a high-risk procedure