creating xml document from string builder returns empty document

Am trying to create am xml document using string builder as follows. string builder having the exact value as expected. but it does not write to the xml file. following is the code

mssql = "select ID, ParentID, OrderID, Title, Start, End, PercentComplete, Expanded, Summary From Project"
        Dim buildXML As New StringBuilder
        buildXML.Append("<?xml version=""1.0"" encoding=""utf-8""?><Project>  <Tasks>")
        Dim mycommand As OdbcCommand
        mycommand = New OdbcCommand(mssql, dbcon)
        dbcon.Open()
        Dim reader As OdbcDataReader
        reader = mycommand.ExecuteReader
        While reader.Read
            buildXML.Append("<Task>" & _
            "<ID>1</ID>" & _
            "<ParentID />" & _
            "<Start>" & reader.Item("Start") & "</Start>" & _
            "<End>" & reader.Item("End") & "</End>" & _
            "<Title>" & reader.Item("Title") & "</Title>" & _
            "<PercentComplete>" & reader.Item("PercentComplete") & "</PercentComplete>" & _
            "<Summary>" & reader.Item("Summary") & "</Summary>" & _
            "<Expanded>" & reader.Item("Expanded") & "</Expanded>" & _
            "<OrderID>" & reader.Item("OrderID") & "</OrderID>" & _
            "</Task>")
        End While
        buildXML.Append("</Tasks>  <Dependencies /></Project>")
        reader.Close()
        dbcon.Close()

        'everything work fine up to this 

        Dim XMLDocument As System.Xml.XmlDocument = New System.Xml.XmlDocument()
        XMLDocument.LoadXml(buildXML.ToString())
        Dim Output As New XmlTextWriter(Server.MapPath("~/App_Data/gantt.xml"), System.Text.Encoding.UTF8)
        XMLDocument.WriteTo(Output)

saving the document will result in empty document, does anyone know the reason?