Arduino Mega 2560 problems with flashing with FLIP

Hello all Im new to Arduino and I want to make a MIDI controller im trying to flash a new version and then MIDI hex file but im getting a eror :
com.atmel.flip.ispException
could not open USB device

I installed the USB port to ATmega8U2 (which is on the Mega 2560 board) and I get this error Please help guys :frowning:

To flash code onto the ATmega8U2, you need to put it into DFU mode by shorting its reset pins while it is plugged in. There ought to be plenty of tutorials on Google.