MSP430G2553 interface with MCP23017 in I2C communication

I am trying to configure the MCP23017 I/O expander with the MSP430G2553 mcu. The I/O expander uses I2C 
and when I try and send data to the device, the mcu only calls the tx interrupt once which never triggers a stop 
condition that is in the ISR for I2C transmit. Please let me know what I am doing wrong.

   
int main(void)
{
    Grace_init();                   // Activate Grace-generated configuration

    UCB0I2CSA = 0x40;				// Configure the Load device
    TxData[0] = 0x00;				// Write to the IODIRA Register
    TxData[1] = 0x00;				// Set all pins in port A as outputs
    TxData[2] = 0x01;				// Write to the IODIRB Register
    TxData[3] = 0x00;				// Set all pins in port B as outputs
    TxData[4] = 0x0C;				// Write to the GPPUA Register
    TxData[5] = 0xFF;				// Enable pull-up resistors on all pins in port A
    TxData[6] = 0x0D;				// Write to the GPPUB Register
    TxData[7] = 0xFF;				// Enable pull-up resistors on all pins in port B

    PTxData = (unsigned char *)TxData;
    TXByteCtr = sizeof TxData;
    UCB0CTL1 |= UCTR + UCTXSTT; // I2C TX, start condition
}



#pragma vector=USCIAB0TX_VECTOR
__interrupt void USCI0TX_ISR_HOOK(void)
{
	if(TXByteCtr) // Check TX Byte byte counter
	{
		UCB0TXBUF = *PTxData++; // Load TX Buffer
		TXByteCtr--;			// Decrement TX byte counter
	}
	else
	{
		UCB0CTL1 |= UCTXSTP; 	// I2C stop condition
		IFG2 &= ~UCTXSTP;		// Clear USCI_B0 TX int flag
		__bic_SR_register_on_exit(LPM0_bits); // Exit LPM if all data was transmitted
	}
}