I need to hide columns in GridView then access the values of these columns in GridViewSelectedIndex using vb.net When I set visible=false for Bound colums i cannot access the values

            <asp:TemplateField Visible=False>
            <ItemTemplate>
            <asp:HiddenField ID=hdnSeqID Value='<%#Eval("Seq_ID") %>' runat=server/>                 
            </ItemTemplate>           

            </asp:TemplateField>

            <asp:TemplateField  HeaderText="FormCode" Visible=false>
            <ItemTemplate>
            <asp:HiddenField ID=hdnFormCode Value='<%#Eval("Form_Code") %>' runat=server/>                 
            </ItemTemplate>           

            </asp:TemplateField>
        </Columns>
        <RowStyle BackColor="#EFF3FB" />
        <EditRowStyle BackColor="#2461BF" />
        <SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" />
        <PagerStyle BackColor="#2461BF" ForeColor="White" HorizontalAlign="Center" />
        <HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
        <AlternatingRowStyle BackColor="White" />
    </asp:GridView>

Protected Sub GridView1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles GridView1.SelectedIndexChanged Dim Instance_ID As String Dim Seq_ID As String Dim Form_Code As String Dim PARMS As String Dim DestinationURL As String Dim DestinationParms As String

    'fill text box's with values from selected row
    ' store values from selected row        
    'Dim instanceID As String = CType(GridView1.SelectedRow.FindControl("hdnInstanceID"), HiddenField).Value
    Dim seqID As String = CType(GridView1.SelectedRow.FindControl("hdnSeqID"), HiddenField).Value

    Dim formCode As String = CType(GridView1.SelectedRow.FindControl("hdnFormCode"), HiddenField).Value