C / C++ / MFC

<br />
//Main.h<br />
CPropertySheet	m_sheet;<br />
CAboutDlg        m_about;<br />
//Main.cpp<br />
...<br />
	m_sheet.AddPage(&m_about);<br />
	m_sheet.Create(this, WS_CHILD|WS_VISIBLE,WS_EX_CONTROLPARENT);<br />
	m_sheet.SetWindowPos(NULL, 4, 4,25, 50, SWP_NOSIZE | SWP_NOZORDER | SWP_NOACTIVATE);<br />
....<br />
//CAbout.cpp<br />
...<br />
        m_sheet = GetPrient();<br />
        CString szDlgName(_T("test"));<br />
	TC_ITEM   TabCtrlItem;     <br />
        TabCtrlItem.mask   =   TCIF_TEXT;     <br />
	TabCtrlItem.dwState   =   TCIS_BUTTONPRESSED;   <br />
	TabCtrlItem.pszText = buf;<br />
<br />
	strcpy(TabCtrlItem.pszText,szDlgName);<br />
<br />
	int index = m_sheet.GetPageIndex(this);//make a Exception<br />
// probably the m_sheet is null caused exception, why it is happened<br />
	m_sheet.GetTabControl()->SetItem(index,&TabCtrlItem);<br />
<br />
...<br />

Hi, 
I need ask the user save what the changes on my app when user exit thep app

I used at bellow but It is not work correctly

bool CTestDLLDlg::CleanUp() 
{
	int iMes=-1;
	if(bHasMouseAdjusted){

		iMes = ::MessageBox(this->m_hWnd,"Don you want to save the changes to Sence Configuration?","Pixelware TV Life",3);
	}

	if(iMes==2){
		return false;
        }
        if(iMes==6){
           //Save what the changes here
        }
    return true;
}

void CTestDLLDlg::OnDestroy() 
{
	// TODO: Add your message handler code here
	if(CleanUp())
	{
		CDialog::OnDestroy();
	}
	
}

void CTestDLLDlg::OnFileExit() 
{
	// TODO: Add your command handler code here
	if(CleanUp())
	{
		PostQuitMessage (1);	
	}
}

This close the app first after show the message box and with OnFileExit this cause system error.
Please help me with this.

Thank in advance!