Arduino SPI not transmitting
I found this on the Arduino SPI page http://arduino.cc/en/Reference/SPI

Note about Slave Select (SS) pin on AVR based boards
All AVR based boards have an SS pin that is useful when they act as a slave controlled by an external master. Since this library supports only master mode, this pin should be set always as OUTPUT otherwise the SPI interface could be put automatically into slave mode by hardware, rendering the library inoperative.
It is, however, possible to use any pin as the Slave Select (SS) for the devices. For example, the Arduino Ethernet shield uses pin 4 to control the SPI connection to the on-board SD card, and pin 10 to control the connection to the Ethernet controller.

Not sure if it will fix the problem, so far most of my boards have used the SS pin as an output regardless.