MSP430F2616: DAC Calibration fail issue

Dear PL:

my customer meet DAC Calibration fail issue during their new product. customer could not implement DAC calibration sucessful during initial stage.customer code as below. could you please help debug it? 

 DAC12_0CTL_bit.DAC12ENC = 0u;       // DAC12 is disabled

 DAC12_1CTL_bit.DAC12ENC = 0u;       // DAC12 is disabled

   // Reset the control registers to thier default power-up states.

   DAC12_0CTL = 0x0000u;

   DAC12_1CTL = 0x0000u;

   DAC12_1CTL_bit.DAC12OPS = 0u;       // outputs: DAC0 = P6.6, DAC1 = P6.7

   DAC12_1CTL_bit.DAC12SREFx = 2u;     // DAC reference = eVref+

   DAC12_1CTL_bit.DAC12RES = 0u;       // 12-bit resolution

   DAC12_1CTL_bit.DAC12LSELx = 0u;     // DAC12 values loaded immediately

   DAC12_1CTL_bit.DAC12IR = 1u;        // DAC output at 1X reference input

   DAC12_1CTL_bit.DAC12AMPx = 7u;      // In/out buffers = high speed/current

   DAC12_1CTL_bit.DAC12DF = 0u;        // staright binary data (0 to 0xFFFF)

   DAC12_1CTL_bit.DAC12IE = 0u;        // DAC12 interrupts disabled

   DAC12_1CTL_bit.DAC12IFG = 0u;       // clear any existing flags

   DAC12_1CTL_bit.DAC12GRP = 0u;       // DAC outputs are not grouped

   DAC12_1DAT = 0u;                    // Set initial output = 0V

   DAC12_1CTL_bit.DAC12ENC = 1u;       // DAC12 is enabled

   DAC12_1CTL_bit.DAC12CALON = 1u;     // Initiate DAC12 Calibration

   // Wait for calibration complete. bit will automatically reset

   do {TEST_HARNESS_TICK;} while(1u == DAC12_1CTL_bit.DAC12CALON);