Why the ShockwaveFlash's WMode variable not working

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C++

Flash

wxWidgets

When I use wxActiveXContainer and ShockwaveFlash ActiveX to display flash media, I set "transparent" to the ShockwaveFlash's "WMode" variable.However,the flash media's background still be rendered. the code:

const CLSID CLSID_ShockwaveFlash = __uuidof(ShockwaveFlash);
const IID   IID_IShockwaveFlash  = __uuidof(IShockwaveFlash);
HRESULT hr = ::CoCreateInstance(CLSID_ShockwaveFlash, NULL, CLSCTX_INPROC_SERVER,
                                IID_IShockwaveFlash, (void **)&m_pFlash);
    if ( FAILED(hr) )
    {
        wxLogSysError(hr, "Failed to create Flash ActiveX control");
        return;
    }
    CMyActiveXContainer *pActive = new CMyActiveXContainer(this, IID_IShockwaveFlash, m_pFlash);
    hr = m_pFlash->LoadMovie(0, m_strSwfFile.wc_str());
    m_pFlash->PutWMode(L"transparent");

The flash media has no problem, I can use the method complete this work.
How to solve the problem???