@billRoy:
Ah, now we are getting somewhere!
It chokes on line 337 just after #define N_WORKED0, the part that starts with #elif defined(AVR_ATmega1280) || defined(AVR_ATmega2560).
So it is still skipping my added #if defined(AVR_ATmega1280_DFR).
The question is why?
Are libraries pre-compiled before the sketch?
And if so is there a way for me make an opt-in alteration that I can enable in the sketch?
@PaulS:
So I included the w5100.h and it makes no difference. Is the order bellow correct?
#define __AVR_ATmega1280_DFR__
#include <SPI.h>
#include <w5100.h>
#include <Ethernet.h>