Tooltip display fails

[yuenqi]

void CMyToolTip::InitToolTip(HWND hParentWnd)
{
    if(m_toolTip.m_hWnd)
    {
        m_toolTip.Create(CWnd::FromHandle(hParentWnd),WS_POPUP|TTS_BALLOON);
        m_toolTip.Activate(FALSE);
    }
}

void CMyToolTip::SetToolTipText(LPCTSTR lpToolTipTxt, HWND hParentWnd, BOOL bActivate)
{
    if(NULL==lpToolTipTxt) return;
    InitToolTip(hParentWnd);
    if(0==m_toolTip.GetToolCount())
    {
        CRect rcPic; 
        ::GetClientRect(hParentWnd,&rcPic);
        m_toolTip.AddTool(CWnd::FromHandle(hParentWnd), lpToolTipTxt, &rcPic,1);
    }
    m_toolTip.Activate(bActivate);
    m_toolTip.UpdateTipText(lpToolTipTxt,CWnd::FromHandle(hParentWnd),1);
} 

I have tried the above code to display a balloon tooltip when my mouse is over the picture control but it doesn't show me anything at all. Could you help me ?

Thanks