msp430f5659: Internal rtc issue

hello,

I am using msp430f5659 micro controller. I am interfacing internal rtc module using the example given by ti. My RTCis working correctly but sometimes it stuck in "do while" loop. I did it on different hardware units but i am facing the same problem on all hardware. I am using a crystal of 32.768KHz.

I am using a battery of 3.6v on vbat pin a capacitor of 470nf is connected to vbak pin. Why is this problem arising? please help me to find the solution of the above problem.

     while(BAKCTL & LOCKBAK)                   // Unlock XT1 pins for operation
         BAKCTL &= ~(LOCKBAK);

      UCSCTL6 &= ~(XT1OFF);                     // XT1 On
      UCSCTL6 |= XCAP_3;                        // Internal load cap
    do
      {
        UCSCTL7 &= ~(XT2OFFG + XT1LFOFFG + DCOFFG);
                                                // Clear XT2,XT1,DCO fault flags
        SFRIFG1 &= ~OFIFG;                      // Clear fault flags
      }while (SFRIFG1&OFIFG);                   // Test oscillator fault flag

      RTCCTL01 |= RTCHOLD + RTCBCD ;  // BCD mode, RTC hold, enable RTC read ready interrupt

      RTCYEAR = 0x2017;                         // Year = 0x2011
      RTCMON = 0x10;                            // Month = 0x06 = June
      RTCDAY = 0x30;                            // Day = 0x22 = 22nd
      RTCDOW = 0x05;                            // Day of week = 0x05 = Friday
      RTCHOUR = 0x14;
      // Hour = 0x11
      RTCMIN = 0x10;                            // Minute = 0x59
      RTCSEC = 0x00;                            // Seconds = 0x45

      RTCCTL01 &= ~(RTCHOLD);                   // Start RTC calendar mode