Lpc2000

I have a problem with a simple SPI example program.
Part: LPC2129
PCK: 14.7 MHz
Mode: Master, CPOL=0, CPHA=0, LSIF=0.

I initialise the SPI like this:-
void SPI_Init(void)
   {
	S0SPCCR = 0x26;	// Divides PCK to give about 400kHz
	S0SPCR = 0x20;	// Select Master mode
   }

And then use the SPI like this:-
void SPI_Transfer( char *buf, int count)
{
	int r = 0, i = 0;

	for( ; i < count; i++ )
	{
		S0SPDR = buf[i];	// Write data
		do{ r = S0SPSR; }while(!(r & 0x80));// Wait for SPIF
		// Read status - to be done
		buf[i] = S0SPDR;	// Read data
	}
}

Sometimes I power up the device and this function runs correctly 
with problem whatsoever. Other times the function just hangs. If I 
attach a JTAG debugger (Keil ULINK) I find that the function is 
hanging at the line "do{ r = S0SPSR; }while(!(r & 0x80));" on the 
first itteration.

There is no hardware attached to the SPI port. I figured that the 
device should put data out onto an unconnected pin without any 
problem and that I should be able to get the software working before 
thinking about ading hardware.

Has anyone got any ideas what might be going wrong?

Thanks,

Paul