Interfacing RTC BQ32000 with MSP430g2553, using interrupts fails on read

#include <msp430.h>
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>

void I2CInit(unsigned char RTC_i2c_address);
void I2CWriteInit(void);
void I2CReadInit(void);

static unsigned char *PRxData;                     // Pointer to RX data
static unsigned char *PTxData;                     // Pointer to RX data
static unsigned char TxByteCtr;
static unsigned char RxByteCtr;
volatile unsigned char TxBuffer[]= {
		  0x00
		};
volatile unsigned char RxBuffer[7];
static volatile unsigned char read_notwrite;

int main(void)
{
		unsigned char Time[7];


		WDTCTL = WDTPW + WDTHOLD;               // Stop WDT
		P1DIR |= 0x01;                          // set P1.0 to output direction
		P1OUT &= ~0x01;                    		// reset P1.0
		I2CInit( 0x68 );						// init RTC


	while (1)
	{
		while(UCB0STAT & UCBBUSY); 				// wait for bus to be free

		read_notwrite=1;
		PTxData = (unsigned char *)TxBuffer;      // TX array start address
		TxByteCtr = sizeof TxBuffer;              // Load TX byte counter
		RxByteCtr = 1;
		while (UCB0CTL1 & UCTXSTP);             // Ensure stop condition got sent
		UCB0CTL1 |= UCTR + UCTXSTT;             // I2C TX, start condition
		__bis_SR_register(CPUOFF + GIE);        // Enter LPM0 w/ interrupts
											  // Remain in LPM0 until all data
											  // is RX'd

	}
}


void I2CInit(unsigned char rtc_i2c_address)
{

	  WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT
	  P1SEL |= BIT6 + BIT7;                     // Assign I2C pins to USCI_B0
	  P1SEL2|= BIT6 + BIT7;                     // Assign I2C pins to USCI_B0
	  UCB0CTL1 |= UCSWRST;                      // Enable SW reset
	  UCB0CTL0 = UCMST + UCMODE_3 + UCSYNC;     // I2C Master, synchronous mode
	  UCB0CTL1 = UCSSEL_2 + UCSWRST;            // Use SMCLK, keep SW reset
	  UCB0BR0 = 20;                             // fSCL = SMCLK/12 = ~100kHz
	  UCB0BR1 = 0;
	  UCB0I2CSA = rtc_i2c_address;                         // Slave Address is 048h
	  UCB0CTL1 &= ~UCSWRST;                     // Clear SW reset, resume operation
	  IE2 |= UCB0TXIE;                          // Enable TX interrupt
	  IE2 |= UCB0RXIE;                          // Enable RX interrupt
}

void I2CWriteInit(void)
{

}

void I2CReadInit(void)
{

}



#pragma vector = USCIAB0TX_VECTOR
__interrupt void USCIAB0TX_ISR(void)
{
	if( read_notwrite == 1 )							// if read
	{
		  if ( TxByteCtr )                              // Check TX byte counter
		  {
				UCB0TXBUF = *PTxData++;                 // Load TX buffer
				TxByteCtr--;                            // Decrement TX byte counter
		  }
		  else
		  {
				UCB0CTL1 &= ~UCTR;						// set read mode
				UCB0CTL1 |= UCTXSTT;                    // I2C stop condition
			  	IE2 &= ~UCB0TXIE;                       // Disable TX interrupt
				IFG2 &= ~UCB0TXIFG;                     // Clear USCI_B0 TX int flag
		  }
	}
}


#pragma vector = USCIAB0RX_VECTOR
__interrupt void USCIAB0RX_ISR(void)
{
	if( read_notwrite == 1 )						// if read
	{
		if( RxByteCtr )								// Check RX byte counter
		{
			P1OUT |= 0x01;                    		// set P1.0 (for testing)
			RxBuffer[RxByteCtr] = UCB0RXBUF;
			RxByteCtr--;
		}
		else
		{
			UCB0CTL1 |= UCTXSTP;				    // stop condition
			IFG2 &= ~UCB0RXIFG;                     // Clear USCI_B0 RX int flag
			__bic_SR_register_on_exit(CPUOFF);      // Exit LPM0 if data was
													// received
		}
	}

}