xml file not saving in app_data in vb.net

If (IO.File.Exists(Server.MapPath("~/App_Data/XMLFile1.xml"))) Then

            Dim document As XmlReader = New XmlTextReader(Server.MapPath("~/App_Data/XMLFile1.xml"))

            While (document.Read())

                Dim type = document.NodeType


                If (type = XmlNodeType.Element) Then

                    If document.Name <> dpFiles.SelectedItem.Text Then

                        Dim innertext As String
                        innertext = document.ReadInnerXml.ToString()

                        Dim filename As String = Server.MapPath("~/App_Data/XMLFile1.xml")

                        'create new instance of XmlDocument
                        Dim doc As New XmlDocument()

                        'load from file
                        doc.Load(filename)
                        Try

                            Dim node As XmlNode = doc.CreateNode(XmlNodeType.Element, "" & dpFiles.SelectedItem.Text & "", Nothing)
                            'node.InnerText = "this is new node";

                            'create title node
                            Dim nodeTitle As XmlNode = doc.CreateElement("" & dpFiles.SelectedItem.Text & "")
                            'add value for it
                            nodeTitle.InnerText = lblRandomNumber.Text

                            'create FileName
                            Dim nodeFileName As XmlNode = doc.CreateElement("FileName")
                            nodeFileName.InnerText = txtFileName.Text

                            'create FilePath
                            Dim nodeFilePath As XmlNode = doc.CreateElement("FilePath")
                            nodeFilePath.InnerText = txtFolderPath.Text

                            'create FileDesc
                            Dim nodeFileDesc As XmlNode = doc.CreateElement("Description")
                            nodeFileDesc.InnerText = txtDesc.Text

                            'add to parent node
                            node.AppendChild(nodeTitle)
                            node.AppendChild(nodeFileName)
                            node.AppendChild(nodeFilePath)
                            node.AppendChild(nodeFileDesc)

                            'add to elements collection
                            doc.DocumentElement.AppendChild(node)

                            'save back
                            doc.Save(filename)
                        Catch ex As Exception
                            MsgBox(ex.ToString())
                        End Try
                    End If
                End If
            End While