Using avrdude to program USB interface on Arduino Uno R3

[CambridgeMart]

I'm tring to program the ATMega 16U2 device on an Uno R3 with the MIDI USB firmware; I'm using avrdude to program the 16U2 via the ICSP header using an Arduino Nano configured as an ISP device. Avrdude is throwing errors indicating it can't sync with the target, but I'm not sure where I'm going wrong. The command I'm using is:
avrdude -p at90usb162 -F -P COM7 -c avrisp -U flash:w:dualMoco.hex -U lfuse:w:0xFF:m -U hfuse:w:0xD9:m -U efuse:w:0xF4:m -U lock:w:0x0F:m
COM7 is the virtual port that my arduino ISP appears as; I'm using at90usb162 to identify the 16U2, based on my research this appears to be the correct target.
The error is avrdude: stk500_getsync(): not in sync: resp=0x00

Any suggestions please?

[Psi]

Is the Arduino Nano frequency correct? 8mhz and 16mhz versions exist.

If there's a mismatch you will have these sort of issues.

Also check your nano has correct reset line and ground connections to target 16u2 device.

[oPossum]

You may have to disable reset on the nano to prevent it from entering the booloader when COM7 is opened.