关于异步串口的一个问题

先贴代码吧，如下：
 if (!ClearCommError(m_hComm, &dwError, &state))
        {
            PurgeComm(m_hComm, PURGE_RXABORT | PURGE_RXCLEAR);
            return -3;
        }        if (!state.cbInQue)
        {
            if (dwWait)
            {
                SetCommMask(m_hComm, EV_RXCHAR | EV_ERR);
                if (!WaitCommEvent(m_hComm, &dwMask, &m_ReadOverlapped))
                {
                    if (GetLastError() == ERROR_IO_PENDING)
                        WaitForSingleObject(m_ReadOverlapped.hEvent, dwWait);
                }                ClearCommError(m_hComm, &dwError, &state);            
            }            if (!state.cbInQue)
                return -4;
        }        if (!ReadFile(m_hComm, lpBuffer, len, &dwRead, &m_ReadOverlapped))
        {
              return -9;        
        }
在执行过程中，cbInQue一直是0，但是监控串口已经读到了正确的数据，每次都是返回-4，请问大侠们，到底是什么原因啊？