Validation failing using cXML

I get his error: "The parameter entity replacement text must nest properly within markup declarations. An error occurred at file:///T:/Clients/L_c/Lone Star Supplies/Invoicer/Invoicer/bin/InvoiceDetail.dtd, (3929, 79)."

 the XML doc: http://qdataviewer.com/downloads/Invoice2.xml

 the dtd doc: http://qdataviewer.com/downloads/InvoiceDetail.dtd

Below is my code:
 
        Dim source As String = AppDomain.CurrentDomain.BaseDirectory & "invoice2.xml"
        Dim XMLDoc2 As Xml.XmlTextReader
        Dim xr As Xml.XmlValidatingReader
        XMLDoc2 = New Xml.XmlTextReader(source)
        xr = New Xml.XmlValidatingReader(XMLDoc2)
        xr.ValidationType = Xml.ValidationType.DTD

        Try
            While xr.Read()
                Debug.Write(i)
                i = i + 1
            End While
            xr.Close()
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try