msxml6.tlh IXMLDOMNode error incomplete type is not allowed from detected during instantiation of class

Question

MSXML2::IXMLDOMDocumentPtr pXMLDom = NULL;

HRESULT hr = CoInitialize(NULL);
hr = pXMLDom.CreateInstance("Msxml2.DOMDocument.6.0");
if (FAILED(hr))
{
    printf("Failed to instantiate an XML DOM.\n");
    return NULL;
}

if (pXMLDom->load(L"dynaDOMsmart.xml") == VARIANT_TRUE) 
{
    printf("XML DOM loaded from dynaDOMsmart.xml:\n%s\n", (LPCSTR)pXMLDom->xml);
    return pXMLDom;
}
else
{
    // Failed to load xml
    printf("Failed to load DOM from dynaDOMsmart.xml. %s\n",
        (LPCSTR)pXMLDom->parseError->Getreason());
}

From a Windows Form Project in C++, I'm trying to load an IXMLDOMDocument using the MSXML2::IXMLDOMDocumentPtr pxmlDomDoc variable. I am getting this error:

incomplete type is not allowed

detected during instantiation of the class.

I dont know why it's occurring, since I did it the same way from a console project in the same language without error.