Error in XML parsing with ATL Server Library

virtual HRESULT BeginParse(IStream *pStream)
{
   ATLASSERT( pStream != NULL );
   CComVariant varStream;
   varStream = static_cast<IUnknown*>pStream);
   HRESULT hr = m_spReader->parse(varStream);
 
   if (SUCCEEDED(hr))
   {
      if (m_refMap.GetCount() != 0)
      {
         hr = E_FAIL;
      }
   }
 
   return hr;
}

When run to m_spReader->parse(varStream), will show error, I don't know why the error happens. Who can tell me. Thank you.