Why does my property sheet has disappeared immediately? [solved]

[PCuong1983]

I have a dialog based application named: basicreport and created one dialog called: CExternalDataDlg , 3 property page called: CImportPage, COptionPage, CConfirmPage and 1 property sheet named: CImportPropertySheet. inside: BOOL CBasicReportApp::InitInstance()

BOOL CBasicReportApp::InitInstance(){
......
CExternalDataDlg dlg;
m_pMainWnd = &dlg;
INT_PTR nResponse = dlg.DoModal();
if (nResponse == IDOK)
{
// TODO: Place code here to handle when the dialog is
// dismissed with OK

}
else if (nResponse == IDCANCEL)
{
	// TODO: Place code here to handle when the dialog is
	//  dismissed with Cancel
	
}
    return FALSE;

}

CExternalDataDlg displayed correctly, worked fine! I have change above code to:

BOOL CBasicReportApp::InitInstance(){
......
CImportPropertySheet importWizardSheet(_T("Import Spreadsheet Wizard"));
CImportPage importpage;
COptionPage optionpage;
CConfirmPage confirmpage;

importWizardSheet.AddPage(&importpage);
importWizardSheet.AddPage(&optionpage);
importWizardSheet.AddPage(&confirmpage);
importWizardSheet.SetWizardMode();


m\_pMainWnd = &importWizardSheet;

INT\_PTR nWizardResponse = importWizardSheet.DoModal();
if(nWizardResponse == ID\_WIZFINISH){
	AfxMessageBox(\_T("Importing..........."));
}
else if(nWizardResponse == IDCANCEL){
	AfxMessageBox(\_T("Cancel"));
}
else{
}
    return FALSE;

}

CImportPropertySheet displayed correctly, worked fine! but when i combinated the both above into once. It looked like

    CExternalDataDlg dlg;
m\_pMainWnd = &dlg;
INT\_PTR nResponse = dlg.DoModal();
if (nResponse == IDOK)
{
	// TODO: Place code here to handle when the dialog is
	//  dismissed with OK
	CImportPropertySheet importWizardSheet(\_T("Import Spreadsheet Wizard"));
	CImportPage importpage;
	COptionPage optionpage;
	CConfirmPage confirmpage;

	importWizardSheet.AddPage(&importpage);
	importWizardSheet.AddPage(&optionpage);
	importWizardSheet.AddPage(&confirmpage);
	importWizardSheet.SetWizardMode();
	
	INT\_PTR nWizardResponse = importWizardSheet.DoModal();
	if(nWizardResponse == ID\_WIZFINISH){
		AfxMessageBox(\_T("Importing..........."));
	}
	else if(nWizardResponse == IDCANCEL){
		AfxMessageBox(\_T("Cancel"));
	}
	else{
	}
}
else if (nResponse == IDCANCEL)
{
	// TODO: Place code here to handle when the dialog is
	//  dismissed with Cancel
	return FALSE;