accessing class member variables from within interrupts

Does anyone know why can't I access member variables from within __interrupt?  

1. I have a class (UARTBuffer) defined as following:
   1. class UARTBuffer: public __HHI__::DataBuffer {
   2. public:
   3.        UARTBuffer();
   4.        virtual ~UARTBuffer();
   5.        void Init();
   6.        void FetchCmdToQueue();
   7.        void SendData(unsigned char *);
   8.        void DispatchCmd(void);
   9.        unsigned char PackDataForRF(char, char, char, void *, char);
   10. private:
   11.        char                 cmdSupported[10];
   12.        _cmdQueue            qList[QUEUE_SIZE];
   13.        _cmdQueue            uartCmd;
   14.        _cmdQueue            uartRcv;
   15.        _respQueue           uartTx;
   16.        char                 RespData[RESP_DATA_SIZE];
   17.        char                 qCount;
   18.        char                 qFront;
   19.        char                 qRear;
   20.        char                 lastRefNum;
   21.        char                 pkRefNum;
   22.        static unsigned char       uartRcvIndex;
   23.        unsigned char        uartTxIndex;
   24.        unsigned char        RespDataCount;
   25.        unsigned char        *ptrUartTx;
   26.        unsigned char        uartStatus;
   27. aa.  

bb. private:

1. cc.        static __interrupt void USCIA1_UART_ISR(void);

dd. };

1. I would like to access its member “uartRcvIndex” in interrupt:
   1. #pragma vector=USCI_A1_VECTOR
   2. __interrupt void UARTBuffer::USCIA1_UART_ISR(void)
   3. {
   4.        motor.DisableInterrupts();
   5.        if (UCA1IFG & UCRXIFG)
   6.        {
   7.               // Handle UART RX event.
   8.               if (uartRcvIndex > CMD_SIZE)
   9.                      uartRcvIndex = 0;
   10. Compiler complains:
       1. undefined                         first referenced            
       2.   symbol                               in file                 
       3.  ---------                         ----------------            
       4.  __HHI__::UARTBuffer::uartRcvIndex ./Source Files/UARTBuffer.obj