Pixhawk 248 Firmware
This is often a driver conflict. Close Mission Planner, unplug the USB cable, reboot the computer, and reconnect. Ensure no other program (like a web browser or terminal) is holding the COM port open.
Ensure your Pixhawk 2.4.8 is not plugged into the USB port yet. pixhawk 248 firmware
Click Yes when prompted to confirm. The firmware will begin downloading and erasing the flash memory before writing the new firmware. This is often a driver conflict