I refer to the older posts 'SPI error' (Author: Sridhar, Posted: 14/12/04) and 'No SPI activity on MCB2100' (Author: Laurens Swaans, Posted: 17/11/05).
I recently viewed these discussions as I was having the same problem, I was unable to get the LPC2129 on the MCB2100 board to output SPI.
The answer is not well documented but you deffinetly do need a pull-up resistor on the SSEL line. After having my code fail for two days, I used a 680 Ohm pulled up to 3.3 Volts on the MCB2100 board and my code worked straight away.
If the SSEL is not pulled up, the LPC2129 goes into slave mode. Awkward wording in the user manual does imply this fact.
This obscurity has apparently been fixed on later devices. I was able to run the same SPI code on the MCB2130 board (with an LPC2138) without the pull-up resistor.