Sometimes this process works:
Press the erase button for 3 seconds, then the reset button for 3 seconds, then select the correct COM port + Arduino DUE (Programming Port) in Menu>Tool>Type of board and upload (hopefully successfully) your sketch.
Sometimes this process works:
Press the erase button for 3 seconds, then the reset button for 3 seconds, then select the correct COM port + Arduino DUE (Programming Port) in Menu>Tool>Type of board and upload (hopefully successfully) your sketch.