CCS5.3 编译报错：.out文件无法创建，求解答

原程序如下：

#include <msp430.h>

extern unsigned char RXData,TXData,TXByteCtr,ATXData[2];

void I2C_Init(unsigned char SlaveAddress)
       {  P3SEL |= 0x03;                            // Assign I2C pins to USCI_B0
       UCB0CTL1 |= UCSWRST;                      // Enable SW reset
       UCB0CTL0 = UCMST + UCMODE_3 + UCSYNC;     // I2C Master, synchronous mode
       UCB0CTL1 = UCSSEL_2 + UCSWRST+UCTR;            // Use SMCLK
       UCB0BR0 = 12;                             // fSCL = SMCLK/12 = ~100kHz
       UCB0BR1 = 0;
       UCB0I2CSA = SlaveAddress;                         // Slave Address is 048h
       UCB0CTL1 &= ~UCSWRST;                     // Clear SW reset, resume operation
       UCB0IE |= UCTXIE+UCRXIE+UCSTPIE; }

void I2C_WriteReg(unsigned char RegAddr, unsigned char Data)    //////////涓婁笅灞侫PI闇?瑕佺敤鍒?
{  TXByteCtr = 2;                          // Load TX byte counter
   ATXData[0]=RegAddr;
   ATXData[1]=Data;

   while (UCB0CTL1 & UCTXSTP);             // Ensure stop condition got sent
   UCB0IE |= UCTXIE;  UCB0CTL1 |= UCTR + UCTXSTT;             // I2C TX, start condition
   __bis_SR_register(LPM0_bits + GIE);     // Enter LPM0 w/ interrupts
   __no_operation();
}
unsigned char I2C_ReadByte()             //////////涓婁笅灞侫PI闇?瑕佺敤鍒?
{
 while (UCB0CTL1 & UCTXSTP);             // Ensure stop condition got sent
 UCB0CTL1 &= ~UCTR;
 UCB0IE &=~ UCTXIE;
 UCB0CTL1 |= UCTXSTT;                    // I2C start condition
 while(UCB0CTL1 & UCTXSTT);              // Start condition sent?
 UCB0CTL1 |= UCTXSTP;
 return RXData;
}
#pragma vector = USCI_B0_VECTOR
__interrupt void USCI_B0_ISR(void)
{
 switch(__even_in_range(UCB0IV,12))
 {  case  0: break;                           // Vector  0: No interrupts
 case  2: break;                           // Vector  2: ALIFG
 case  4: break;                           // Vector  4: NACKIFG
 case  6: break;                           // Vector  6: STTIFG
 case  8:
  UCB0IFG &= ~UCSTPIFG;                   // Clear stop condition int flag
  __bic_SR_register_on_exit(LPM0_bits);   // Exit LPM0 if data was transmitted
  break;                           // Vector  8: STPIFG
 case 10:
  RXData=UCB0RXBUF;   // UCB0CTL1 |= UCTXNACK+UCTXSTP;
  UCB0IFG &= ~UCRXIFG;
  __bic_SR_register_on_exit(LPM0_bits);
  break;                           // Vector 10: RXIFG
 case 12:                                  // Vector 12: TXIFG
  if (TXByteCtr)                          // Check TX byte counter
   {
    UCB0TXBUF = ATXData[2-TXByteCtr];                   // Load TX buffer
    TXByteCtr--;                          // Decrement TX byte counter
    }
  else
  {      UCB0CTL1 |= UCTXSTP;                  // I2C stop condition
  UCB0IFG &= ~UCTXIFG;                  // Clear USCI_B0 TX int flag
  __bic_SR_register_on_exit(LPM0_bits); // Exit LPM0
  }
  break;
  default: break;  }}

int main(void) {
    WDTCTL = WDTPW | WDTHOLD; // Stop watchdog timer
   
 return 0;
}

这里是报错：

#10010errors encountered during linking；"I2C.out" not built

#10234-D unresolved symbols remain

请指点，谢谢