Lpc2000

Can someone help me with this problem?  See the code below.  I have
UART1 set up to print "Hello Test", but I can't get it to work with a
12Mhz clock, which is what is on the Eval boards.  I am using
currently the Embedded Artists board with the 12Mhz clock.  If I set
the U1DLL to 0x61, which is a 15Mhz clock, and leave VPBDIV = 0 (1/4
processor clock) it works fine (as in the code below).  If I set
VPBDIV = 1 (equal to the processor clock), or if I set the U1DLL to a
value for 12Mhz, it stops working.  So, I guess I don't quite
understand how all those registers work.  Can someone explain?  Is
there something in the Startup code that overrides?  Thanks.

char txbuffer[25];

void my_putchar(char c)
{
   while((U1LSR & 0x20) == 0);    // if not empty, wait
   U1THR = c;
}

void myprint()				  
{
    unsigned char i;

	i = 0;
	while (i < strlen(txbuffer))
	{
       if (((U1LSR & 0x20) != 0) && txbuffer[i])
       {
          U1THR = txbuffer[i++];
       }
	}
}


void set_up_uart1()
{
   // VPBDIV = 1;     // VPB clk (PCLK) same as processor clock (CCLK)
   PLL0CON = 0;    // not using PLL, since PCLK = oscillator clock
   PLL1CON = 0;    // not used
     
   PINSEL0 |= 0x00010000;
   PCONP |= 0x00000010;

   U1LCR |= 0x80;	       // enable Divisor Latches
   U1FDR = 0x00000010;         // MULVAL = 1, DIVVAL = 0
   U1DLM = 0;	               // 15000000 / 9600 / 16 = 97 = 0x61
   U1DLL = 0x61;	       // 9600 baud, but at 15Mhz
   U1LCR = 0x03;               // 8 bits, 1 stop, no parity, DLAB = 0

   U1FCR = 1;
} 


void 
main()
{
   set_up_uart1();
   sprintf(txbuffer, "Hello Test\r\n");
   while(1)
   {
      myprint();
   }
}