MSComm控件编程有关问题

求助MSComm控件编程问题。
这是我所写的代码，运行后出现Operation not valid while the port is opened。
// 串口界面Dlg.cpp : implementation file
//

#include "stdafx.h"
#include "串口界面.h"
#include "串口界面Dlg.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif

/////////////////////////////////////////////////////////////////////////////
// CAboutDlg dialog used for App About

class CAboutDlg : public CDialog
{
public:
CAboutDlg();

// Dialog Data
//{{AFX_DATA(CAboutDlg)
enum { IDD = IDD_ABOUTBOX };
//}}AFX_DATA

// ClassWizard generated virtual function overrides
//{{AFX_VIRTUAL(CAboutDlg)
protected:
virtual void DoDataExchange(CDataExchange* pDX); // DDX/DDV support
//}}AFX_VIRTUAL

// Implementation
protected:
//{{AFX_MSG(CAboutDlg)
//}}AFX_MSG
DECLARE_MESSAGE_MAP()
};

CAboutDlg::CAboutDlg() : CDialog(CAboutDlg::IDD)
{
//{{AFX_DATA_INIT(CAboutDlg)
//}}AFX_DATA_INIT
}

void CAboutDlg::DoDataExchange(CDataExchange* pDX)
{
CDialog::DoDataExchange(pDX);
//{{AFX_DATA_MAP(CAboutDlg)
//}}AFX_DATA_MAP
}

BEGIN_MESSAGE_MAP(CAboutDlg, CDialog)
//{{AFX_MSG_MAP(CAboutDlg)
// No message handlers
//}}AFX_MSG_MAP
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////////
// CMyDlg dialog

CMyDlg::CMyDlg(CWnd* pParent /*=NULL*/)
: CDialog(CMyDlg::IDD, pParent)
{
//{{AFX_DATA_INIT(CMyDlg)
m_strRXData = _T("");
m_strTXData1 = _T("01");
m_strTXData2 = _T("02");
//}}AFX_DATA_INIT
// Note that LoadIcon does not require a subsequent DestroyIcon in Win32
m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME);
}

void CMyDlg::DoDataExchange(CDataExchange* pDX)
{
CDialog::DoDataExchange(pDX);
//{{AFX_DATA_MAP(CMyDlg)
DDX_Control(pDX, IDC_MSCOMM1, m_ctrlComm);
DDX_Text(pDX, IDC_EDIT_MssageBox, m_strRXData);
//}}AFX_DATA_MAP
}

BEGIN_MESSAGE_MAP(CMyDlg, CDialog)
//{{AFX_MSG_MAP(CMyDlg)
ON_WM_SYSCOMMAND()
ON_WM_PAINT()
ON_WM_QUERYDRAGICON()
ON_BN_CLICKED(IDC_BUTTON_StartA, OnStartA)
ON_BN_CLICKED(IDC_BUTTON_StartB, OnStartB)
//}}AFX_MSG_MAP
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////////
// CMyDlg message handlers

BOOL CMyDlg::OnInitDialog()
{
CDialog::OnInitDialog();

// Add "About..." menu item to system menu.

// IDM_ABOUTBOX must be in the system command range.
ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX);
ASSERT(IDM_ABOUTBOX < 0xF000);

CMenu* pSysMenu = GetSystemMenu(FALSE);
if (pSysMenu != NULL)
{
CString strAboutMenu;
strAboutMenu.LoadString(IDS_ABOUTBOX);
if (!strAboutMenu.IsEmpty())
{
pSysMenu->AppendMenu(MF_SEPARATOR);
pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
}
}

// Set the icon for this dialog. The framework does this automatically
// when the application's main window is not a dialog
SetIcon(m_hIcon, TRUE); // Set big icon
SetIcon(m_hIcon, FALSE); // Set small icon

// TODO: Add extra initialization here
m_ctrlComm.SetCommPort(1); //选择com1
if( !m_ctrlComm.GetPortOpen())
m_ctrlComm.SetPortOpen(TRUE);//打开串口
else
AfxMessageBox("cannot open serial port");

m_ctrlComm.SetInBufferSize(1024);
m_ctrlComm.SetOutBufferSize(512);

m_ctrlComm.SetSettings("9600,n,8,1"); //波特率9600，无校验，8个数据位，1个停止位 

m_ctrlComm.SetInputMode(1); //1：表示以二进制方式检取数据
m_ctrlComm.SetRThreshold(1);