LPC2138 UART irq problem

void UARTInit(unsigned long baudrate)
{
  	volatile char dummy;
	unsigned long Fdiv;
	PCONP |= (1<<4); 
	PINSEL0 |= 0x00050000;
   	
	U1LCR = 0x83;                        /* DLAB =1, STOP =1, NO PARIY, WORD LENGTH = 8 */
	
	Fdiv = ( 15000000UL / 16 ) / baudrate ;	 /* baud rate */
	U1DLM = Fdiv / 256;							
        U1DLL = Fdiv % 256;	
        U1LCR = 0x03;                                                    /* DLAB = 0 */
        U1FCR = 0x07;		                                       /* Enable and reset TX and RX FIFO. */

        VICVectAddr7 = (unsigned long)UART1Handler;          /* set interrupt vector 2 to UART0_IRQHandler interrupt function*/
	VICVectCntl7 = (0x20 | 7);                                    /* enable slot & use it for UART0 Interrupt */
	VICIntEnable |= (unsigned long)(1<<7);                   /* Enable UART0 Interrupt */

  	dummy = U1IIR;                                                   /* Read IrqID - Required to Get Interrupts Started */

	U0IER = IER_RBR | IER_THRE | IER_RLS;	                /* Enable UART0 interrupt */
}



__irq void UART1Handler (void)  
{
  unsigned char IIRValue, LSRValue;

  IIRValue = U1IIR;
    
  IIRValue >>= 1;			/* skip pending bit in IIR */
  IIRValue &= 0x07;			/* check bit 1~3, interrupt identification */

  if ( IIRValue == IIR_THRE )	/* THRE, transmit holding register empty */
  {
	/* THRE interrupt */
	LSRValue = U1LSR;		/* Check status in the LSR to see if
								valid data in U0THR or not */
	if ( LSRValue & LSR_THRE )	 // if(transmitter empty)
	{
	  UART1TxEmpty = 1;		  //empty
	}
	else
	{
	  UART1TxEmpty = 0;		  //char  available
	}
  }
  VICVectAddr = 0;		/* Acknowledge Interrupt */
}



void UARTSend( unsigned char *BufferPtr)
{

	while (*BufferPtr)
    {
	  
	  while ( !(UART1TxEmpty & 0x01) );	/*THRE status, contain valid data */
	  U1THR = *BufferPtr;
	  UART1TxEmpty = 0;	                        /*not empty in the THR until it shifts out */
	  BufferPtr++;
    }
}