TreeView ondemand is not working

<%@ Page Title="" Language="VB" MasterPageFile="~/Site.master" AutoEventWireup="false"
    CodeFile="KB.aspx.vb" Inherits="KB" %>

<asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" runat="Server">
    <style type="text/css">
        .style1
        {
            height: 230px;
        }
        .style2
        {
            width: 157px;
        }
        .myclass { font-size: 1.17em;text-decoration: none;color: #333399; background-color:Blue;}
    </style>



</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="Server">
    <asp:ScriptManager ID="scriptAP" runat="server">
    </asp:ScriptManager>
    <asp:UpdatePanel ID="upDemo" runat="server" UpdateMode="Always" ChildrenAsTriggers="true">
        <ContentTemplate>
            <table>
                <tr>
                    <td valign="top">
                        <asp:TreeView ID="LinksTreeView" Font-Names="Arial" ForeColor="Blue" EnableClientScript="false"
                            OnTreeNodePopulate="PopulateNode" runat="server">
                            <Nodes>
                                <asp:TreeNode Text="Form" SelectAction="Expand" PopulateOnDemand="true" />
                            </Nodes>
                        </asp:TreeView>
                    </td>
                    <td valign="top">
                        <asp:GridView ID="gvDemo" DataKeyNames="ID" HorizontalAlign="Center" runat="server"
                            AllowPaging="True" AutoGenerateColumns="False" CellPadding="3" Font-Names="Verdana"
                            Font-Size="8pt" BorderWidth="0px" Width="700px" Visible="false">
                            <Columns>
                                <asp:BoundField HeaderText="" DataField="Desc" ControlStyle-Width="700" />
                                <asp:TemplateField HeaderText="">
                                    <ItemTemplate>
                                        <asp:LinkButton ID="btnEdit" runat="server" Text="Edit" CssClass="myclass" CommandName="KBEDIT" CommandArgument='<%# DataBinder.Eval(Container.DataItem,"id")%>'
                                            CausesValidation="false" />
                                        <asp:LinkButton ID="btnAddPost" runat="server" Text="AddPost" CommandName="KBPOST"  CssClass="myclass"
                                            CommandArgument='<%# DataBinder.Eval(Container.DataItem,"id")%>' CausesValidation="false" />
                                    </ItemTemplate>
                                </asp:TemplateField>
                            </Columns>
                            <%-- <HeaderStyle BackColor="#0681DF" ForeColor="White" />--%>
                            <%--  <AlternatingRowStyle BackColor="#F5F4F0" />--%>
                        </asp:GridView>
                    </td>
                </tr>
                <tr>
                    <td colspan="2" valign="top">
                        <asp:Panel ID="plnAddPost" runat="server">
                            <table>
                                <tr>
                                    <td>
                                        <asp:Label ID="lblSelectedRow" runat="server" Text=""></asp:Label>
                                    </td>
                                </tr>
                                <tr>
                                    <td>
                                        <asp:DropDownList ID="ddlcategory" runat="server" AutoPostBack="true">
                                        </asp:DropDownList>
                                    </td>
                                    <td>
                                        <asp:DropDownList ID="ddlsubcategory" runat="server">
                                        </asp:DropDownList>
                                    </td>
                                </tr>
                                <tr>
                                    <td colspan="2">
                                        <asp:TextBox ID="txtAddPost" runat="server" TextMode="MultiLine" Width="500" Height="200"></asp:TextBox>
                                        <asp:RequiredFieldValidator ID="RequiredFieldValidator1" ControlToValidate="txtAddPost"
                                            runat="server" ErrorMessage="RequiredFieldValidator"></asp:RequiredFieldValidator>
                                    </td>
                                </tr>
                                <tr>
                                    <td>
                                        <asp:LinkButton ID="btnAddPost" runat="server" Text="AddPost" CssClass="myclass" />
                                    </td>
                                    <td>
                                        <asp:LinkButton ID="btnCancle" runat="server" CssClass="myclass" CausesValidation="false" >Cancle</asp:LinkButton>
                                    </td>
                                </tr>
                            </table>
                        </asp:Panel>
                    </td>
                </tr>
            </table>
            <asp:HiddenField ID="hidnodeid" runat="server" />
        </ContentTemplate>
        <Triggers>
            <asp:AsyncPostBackTrigger ControlID="gvDemo" EventName="PageIndexChanging" />
            <asp:AsyncPostBackTrigger ControlID="gvDemo" EventName="RowCommand" />
            <asp:AsyncPostBackTrigger ControlID="gvDemo" EventName="RowDataBound" />
            <asp:AsyncPostBackTrigger ControlID="btnAddPost" EventName="Click" />
            <asp:AsyncPostBackTrigger ControlID="btnCancle" EventName="Click" />
            <asp:AsyncPostBackTrigger ControlID="ddlcategory" EventName="SelectedIndexChanged" />
            <asp:AsyncPostBackTrigger ControlID="ddlsubcategory" EventName="SelectedIndexChanged" />
        </Triggers>
    </asp:UpdatePanel>
</asp:Content>

Imports System
Imports System.Data
Imports System.Data.OleDb
Partial Class KB
    Inherits System.Web.UI.Page
    Dim objKBlist As New List(Of Knowledge)
    Dim cnn As New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\test.mdb")

    Sub PopulateNode(ByVal sender As Object, ByVal e As TreeNodeEventArgs)

        ' Call the appropriate method to populate a node at a particular level.
        Select Case e.Node.Depth

            Case 0
                ' Populate the first-level nodes.
                PopulateCategories(e.Node)

            Case 1
                ' Populate the second-level nodes.
                PopulateProducts(e.Node)

            Case Else
                ' Do nothing.

        End Select

    End Sub

    Sub PopulateCategories(ByVal node As TreeNode)

        ' Query for the product categories. These are the values
        ' for the second-level nodes.
        Dim ResultSet As DataSet = RunQuery("select ID,name from MasterKB")

        ' Create the second-level nodes.
        If ResultSet.Tables.Count > 0 Then

            ' Iterate through and create a new node for each row in the query results.
            ' Notice that the query results are stored in the table of the DataSet.
            Dim row As DataRow

            For Each row In ResultSet.Tables(0).Rows

                ' Create the new node. Notice that the CategoryId is stored in the Value property
                ' of the node. This will make querying for items in a specific category easier when
                ' the third-level nodes are created.
                Dim NewNode As TreeNode = New TreeNode(row("name").ToString(), row("ID").ToString())

                ' Set the PopulateOnDemand property to true so that the child nodes can be
                ' dynamically populated.
                NewNode.PopulateOnDemand = True

                ' Set additional properties for the node.
                NewNode.SelectAction = TreeNodeSelectAction.Expand

                ' Add the new node to the ChildNodes collection of the parent node.
                node.ChildNodes.Add(NewNode)

            Next

        End If

    End Sub

    Sub PopulateProducts(ByVal node As TreeNode)

        ' Query for the products of the current category. These are the values
        ' for the third-level nodes.
        Dim ResultSet As DataSet = RunQuery("select ID,name from MasterCT where KBID=" & node.Value)

        ' Create the third-level nodes.
        If ResultSet.Tables.Count > 0 Then

            ' Iterate through and create a new node for each row in the query results.
            ' Notice that the query results are stored in the table of the DataSet.
            Dim row As DataRow

            For Each row In ResultSet.Tables(0).Rows

                ' Create the new node.
                Dim NewNode As TreeNode = New TreeNode(row("name").ToString())

                ' Set the PopulateOnDemand property to false because these are leaf nodes and
                ' do not need to be populated.
                NewNode.PopulateOnDemand = False

                ' Set additional properties for the node.
                ' NewNode.SelectAction = TreeNodeSelectAction.None
                NewNode.NavigateUrl = "~/KB.aspx?node=" & row("ID").ToString()
                ' Add the new node to the ChildNodes collection of the parent node.
                node.ChildNodes.Add(NewNode)

            Next

        End If

    End Sub

    Function RunQuery(ByVal QueryString As String) As DataSet

        ' Declare the connection string. This example uses Microsoft SQL Server and connects to the
        ' Northwind sample database.
        'Dim ConnectionString As String = "server=localhost;database=NorthWind;Integrated Security=SSPI"

        'Dim DBConnection As SqlConnection = New SqlConnection(ConnectionString)
        'Dim DBAdapter As SqlDataAdapter
        Dim ResultsDataSet As DataSet = New DataSet


        ' Dim cmd As New OleDbCommand
        Dim DBAdapter As New OleDbDataAdapter
        'Dim dtTable As New DataTable
        'Dim query As String
        'query = "select ID,name from MasterCT where KBID=" & ID
        'cmd = New OleDb.OleDbCommand(query, cnn)
        cnn.Open()
        'Dim myReader As OleDbDataReader = cmd.ExecuteReader()
        'While myReader.Read()
        '    If Not IsDBNull(myReader(0)) Then
        '        ddlsubcategory.Items.Add(New ListItem With {.Value = myReader(0), .Text = myReader(1)})
        '    End If
        'End While
        'cnn.Close()


        Try

            ' Run the query and create a DataSet.
            DBAdapter = New OleDbDataAdapter(QueryString, cnn)
            DBAdapter.Fill(ResultsDataSet)

            ' Close the database connection.
            cnn.Close()

        Catch ex As Exception

            ' Close the database connection if it is still open.
            If cnn.State = ConnectionState.Open Then

                cnn.Close()

            End If

            '   Message.Text = "Unable to connect to the database."

        End Try

        Return ResultsDataSet

    End Function

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Request.QueryString("node") IsNot Nothing Then
            hidnodeid.Value = Request.QueryString("node")
        End If
        If Not Page.IsPostBack Then
            fillGrid()
            fillcategory()
            If Request.QueryString("id") IsNot Nothing Then
                LinksTreeView.Visible = False
                gvDemo.Visible = False
                plnAddPost.Visible = True
                SelectedRowFrom(Request.QueryString("id"))
            Else
                LinksTreeView.Visible = True
                gvDemo.Visible = True
                plnAddPost.Visible = False
            End If
        End If

    End Sub
    Sub fillcategory()
        ddlcategory.Items.Clear()
        Dim cmd As New OleDbCommand
        Dim dtTable As New DataTable
        Dim query As String
        query = "select ID,name from MasterKB"
        cmd = New OleDb.OleDbCommand(query, cnn)
        cnn.Open()
        Dim myReader As OleDbDataReader = cmd.ExecuteReader()
        While myReader.Read()
            If Not IsDBNull(myReader(0)) Then
                ddlcategory.Items.Add(New ListItem With {.Value = myReader(0), .Text = myReader(1)})
            End If
        End While
        cnn.Close()
    End Sub
    Sub fillsubcategory(ByVal id As Integer)
        ddlsubcategory.Items.Clear()
        Dim cmd As New OleDbCommand
        Dim dtTable As New DataTable
        Dim query As String
        query = "select ID,name from MasterCT where KBID=" & id
        cmd = New OleDb.OleDbCommand(query, cnn)
        cnn.Open()
        Dim myReader As OleDbDataReader = cmd.ExecuteReader()
        While myReader.Read()
            If Not IsDBNull(myReader(0)) Then
                ddlsubcategory.Items.Add(New ListItem With {.Value = myReader(0), .Text = myReader(1)})
            End If
        End While
        cnn.Close()
    End Sub
    Sub SelectedRowFrom(ByVal id As Integer)
        Dim cmd As New OleDbCommand
        Dim dtTable As New DataTable
        Dim query As String
        query = "select KB.ID,MasterCT.KBID,KB.CTID,KB.Desc from KB inner join MasterCT on MasterCT.id =KB.CTID where KB.id=" & id
        cmd = New OleDb.OleDbCommand(query, cnn)
        cnn.Open()
        Dim myReader As OleDbDataReader = cmd.ExecuteReader()
        Dim objknowledge As New Knowledge
        While myReader.Read()
            If Not IsDBNull(myReader(0)) Then
                objknowledge.id = myReader(0)
            End If
            If Not IsDBNull(myReader(1)) Then
                objknowledge.kb_id = myReader(1)
            End If

            If Not IsDBNull(myReader(2)) Then
                objknowledge.cb_id = myReader(2)
            End If
            If Not IsDBNull(myReader(3)) Then
                objknowledge.Desc = myReader(3)
            End If
        End While
        cnn.Close()

        With objknowledge
            ddlcategory.SelectedItem.Value = .kb_id
            fillsubcategory(ddlcategory.SelectedItem.Value)
            ddlsubcategory.SelectedItem.Value = .cb_id
            lblSelectedRow.Text = .Desc
        End With
    End Sub
    Sub fillGrid()
        Dim cmd As New OleDbCommand
        Dim dtTable As New DataTable
        Dim query As String
        If hidnodeid.Value <> "" Then
            query = "select ID,CTID,Desc from KB where CTID=" & hidnodeid.Value
        Else
            query = "select ID,CTID,Desc from KB"
        End If

        cmd = New OleDb.OleDbCommand(query, cnn)
        cnn.Open()
        Dim myReader As OleDbDataReader = cmd.ExecuteReader()
        While myReader.Read()
            Dim objKB As New Knowledge
            Dim objKBforPostInformation As New Knowledge
            If Not IsDBNull(myReader(0)) Then
                objKB.id = myReader(0)
                objKBforPostInformation.id = myReader(0)
            End If
            If Not IsDBNull(myReader(1)) Then
                objKB.cb_id = myReader(1)
                objKBforPostInformation.cb_id = myReader(1)
            End If
            If Not IsDBNull(myReader(2)) Then
                objKB.Desc = myReader(2)
                objKBforPostInformation.Desc = ""
            End If
            objKBlist.Add(objKB)
            objKBlist.Add(objKBforPostInformation)
        End While
        cnn.Close()

        '  ViewState.Add("ViewKBlist", objKBlist)
        gvDemo.DataSource = objKBlist
        gvDemo.DataBind()
    End Sub
    Protected Sub gvDemo_PageIndexChanging(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewPageEventArgs) Handles gvDemo.PageIndexChanging
        gvDemo.PageIndex = e.NewPageIndex
        fillGrid()
    End Sub
    Protected Sub gvDemo_RowCommand(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewCommandEventArgs) Handles gvDemo.RowCommand
        Select Case e.CommandName
            Case "KBEDIT"
                Response.Write("select")
            Case "KBPOST"
                Response.Redirect("~/KB.aspx?id=" & e.CommandArgument & "&op=AddPost")
        End Select
    End Sub
    Protected Sub gvDemo_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles gvDemo.RowDataBound
        If e.Row.RowType = DataControlRowType.DataRow Then
            Dim btnEditButton As LinkButton = CType(e.Row.FindControl("btnEdit"), LinkButton)
            Dim btnAddPostButton As LinkButton = CType(e.Row.FindControl("btnAddPost"), LinkButton)
            If e.Row.Cells(0).Text = "" Or e.Row.Cells(0).Text = "&nbsp;" Then
                btnEditButton.Visible = False
                btnAddPostButton.Visible = True
            Else
                ' e.Row.Cells(0).Text = HttpUtility.HtmlDecode(e.Row.Cells(0).Text.Substring(0, 1000)) & "............"
                e.Row.Cells(0).Text = HttpUtility.HtmlDecode(e.Row.Cells(0).Text)

                If Session("userDetails") IsNot Nothing Then
                    btnEditButton.Visible = True
                Else
                    btnEditButton.Visible = False
                End If
                btnAddPostButton.Visible = False
            End If
        End If
    End Sub
    Protected Sub btnCancle_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnCancle.Click
        Response.Redirect("~/KB.aspx")
    End Sub

    Protected Sub ddlcategory_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ddlcategory.SelectedIndexChanged
        fillsubcategory(ddlcategory.SelectedItem.Value)
    End Sub

    Protected Sub btnAddPost_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnAddPost.Click
        If txtAddPost.Text = "" Then
            RequiredFieldValidator1.IsValid = False
        Else
            Dim cmd As New OleDbCommand
            Dim dtTable As New DataTable
            Dim query As String
            query = "INSERT into KB (CTID,[Desc]) Values(" & ddlsubcategory.SelectedItem.Value & ",'" & txtAddPost.Text & "');"
            cmd = New OleDb.OleDbCommand(query, cnn)
            cmd.CommandType = CommandType.Text
            cmd.CommandText = query
            cnn.Open()
            Using cnn
                cmd.ExecuteNonQuery()
            End Using
            cnn.Close()
            Response.Redirect("~/KB.aspx")
        End If

    End Sub
End Class