Because the node I am trying to add is within a namespace, I need to pass it to the method. So, I adjusted the method like this:

        ' Add an element
        ' expC1 Node
        ' expC2 Element
        ' expC3 Namespace
        '       Optional
        Public Function AddXMLElement(ByVal tcNode As String, ByVal tcElement As String, _
         Optional ByVal tcNamespace As String = "") As Boolean

            ' Create the node
            Try
                oXmlElement = oXmlDocument.CreateElement(tcElement, tcNamespace)
            Catch loError As Exception
                cMessage = loError.Message
                Return False
            End Try

            ' Select the node
            If oXmlNameSpaceManager Is Nothing Then
                oXmlNode = oXmlDocument.SelectSingleNode(tcNode)
            Else
                oXmlNode = oXmlDocument.SelectSingleNode(tcNode, oXmlNameSpaceManager)
            End If

            ' See if we obtained the node
            If oXmlNode Is Nothing Then
                cMessage = oApp.StrTran(cNodeDoesNotExist, "##Node##", tcNode)
                Return False
            End If

            ' Add the node
            oXmlNode.AppendChild(oXmlElement)

            cXml = oXmlDocument.OuterXml
            Return True
        End Function

Thus, I obtain:

<ReferenceInfo/>