exception error while automating pp using mfc

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MFC

i`m trying to learn about automating powerpoint using mfc,but my program is not executing properly plz help,here is my code

LPDISPATCH		lpDispatch	= NULL;
	LPUNKNOWN		lpUnk		= NULL;
	HRESULT			hResult		= 0;
	CLSID			clsid		= {0};

	try
	{


	hResult = CLSIDFromProgID( L"PowerPoint.Application", &clsid);
    hResult = GetActiveObject( clsid, NULL,&lpUnk);
	if( hResult != 0)
	{
		hResult = CoCreateInstance( clsid, NULL, CLSCTX_LOCAL_SERVER, IID_IUnknown, (void **)&lpUnk);
	}

	hResult = lpUnk->QueryInterface( IID_IDispatch, (void **) &lpDispatch);
	lpUnk->Release();

	_Application theApp(lpDispatch);

    lpDispatch = theApp.GetPresentations();

	Presentations thePresentations(lpDispatch);
	lpDispatch = thePresentations.Add(0);
	}
	catch(...)
	{
	}