The connection diagram on the linked page is for an UNO. The SPI pins of the Mega are not on pin 10-13. You should use pin 10 for SS but SCK, MISO and MOSI are available on the ICSP connector (the 6 pin connector in the middle of the Mega board) or alternatively on pin 50 (MISO), 51 (MOSI) and 52 (SCK).