hi louis,

o.k lets go on step back.

i think @dhunt has the solution

"...

Ah yes, dfu-programmer 0.5.4 does not know about the atmega16u2 and the developers don't seem to have updated it yet.

Download the dfu-programmer source from Atmel USB DFU Programmer download | SourceForge.net, apply the attached patch and build your own:
Code:
tar xzf ~/Downloads/dfu-programmer-0.5.4.tar.gz
cd dfu-programmer-0.5.4
patch -p0 < ~/Downloads/atmega16u2.diff

Make sure you have the tools needed to build it

sudo apt-get install build-essential libusb-1.0-0-dev

configure and build it

./bootstrap.sh
./configure
make

install it

sudo make install

"""

this is the error i get when trying to install libusb:

Claudio-MacBook-Pro:dfu-programmer-0.5.4 claudiobattista$ sudo apt-get install build-essential libusb-1.0-0-dev
Password:
sudo: apt-get: command not found

seems like i dont have the tool i need?!