Arduino W5500 Ethernet + POE => Issue with External ISP Programmer

Hi,

i bought 3x of this Arduino with W5500 Ethernet + POE module :

https://www.dfrobot.com/product-1286.html

This Arduino is like a Leonardo ETH clone with POE. It uses the ATMEGA32u4 chip.

I can program them using the Arduino IDE or the Visual Micro plugin without issue using an USB cable.

Since this chip has 32kb for flash and the bootloader is taking 4k, i would like to free up the 4k to have more program space.

To do so, we must use an External ISP Programmer as the "Sparkfun Pocket AVR Programmer" from this link : 

https://www.sparkfun.com/products/9825

I can successfully use this External ISP with my other Arduino Boards like my Uno Rev3.
I tried using the same method for the Arduino with W5500 and POE without success.

I also tried using my ARduino Uno Rev3 as an ISP Programmer using the example ArduinoISP sketch. Samething. i can't program the Arduino with W5500 and POE.

The board I am using in the ARduino IDE is "Leonardo ETH" or "Leonardo".
The programmer I am using is the "USBTinyISP".

The error I have have from the Arduino IDE is :
avrdude: programmer operation not supported

avrdude: Using SCK period of 10 usec
avrdude: initialization failed, rc=-1
Double check connections and try again, or use -F to override
this check.

Has someone managed to program this Arduino Board using an external programmer ? If yes...how ?

I also tried the "blink" sketch on the D14, D15 and D16 to ensure that thoses pins react correctly (they are on the ICSP header) and they do. I only noticed that if the led is connected on D14, it is dimmer than on D15/D16 (normal ?). 

Need help please

Thank you.

FranK.