Here the solution to run Arduino Mega and the shield W5100.

Into the file MyConfig.h, after the line:
#include <stdint.h>:

you must add the following lines:

#if ARDUINO < 100
	#include <WProgram.h>
#else
       #include <Arduino.h>
#endif

Then replace the lines:

const uint8_t SOFT_SPI_MISO_PIN = 16;
const uint8_t SOFT_SPI_MOSI_PIN = 15;
const uint8_t SOFT_SPI_SCK_PIN = 14;

with these:

const uint8_t SOFT_SPI_MISO_PIN = A2;
const uint8_t SOFT_SPI_MOSI_PIN = A1;
const uint8_t SOFT_SPI_SCK_PIN = A0;

Finally enable define SOFTSPI removing the comment (//)

Compile and load the software and you're done! :grin: