I am getting error in timer tick event

<%@ Page Title="" Language="C#" MasterPageFile="~/Site.Master" AutoEventWireup="true" CodeBehind="L_PaperSet.aspx.cs" Inherits="Lib_Web.WebForm2" %>
<asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" runat="server">
    <style type="text/css">
        .style7
        {
            width: 100%;
        }
        .style8
        {
            width: 228px;
        }
    </style>
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
    <table class="style7">
        <tr>
            <td class="style8">
                &nbsp;</td>
            <td>
                <asp:ScriptManager ID="ScriptManager1" runat="server">
                </asp:ScriptManager>
                <asp:UpdatePanel ID="UpdatePanel1" runat="server">
                    <ContentTemplate>

                        <asp:Timer ID="Timer1" runat="server" ontick="Timer1_Tick">
                        </asp:Timer>
                        <asp:Image ID="Image1" runat="server" />
                    </ContentTemplate>


                </asp:UpdatePanel>

            </td>
        </tr>
        <tr>
            <td class="style8">
                &nbsp;</td>
            <td>
                &nbsp;</td>
        </tr>
    </table>
</asp:Content>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace Lib_Web
{
    public partial class WebForm2 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                NewMethod();

            }
        }

        protected void Timer1_Tick(object sender, EventArgs e)
        {
            NewMethod();
        }

        private void NewMethod()
        {
            Random rand = new Random();
            int i = rand.Next(1, 4);
            Image1.ImageUrl = "~/L_pics/" + i.ToString() + ".jpg";
        }
    }
}

Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately. 

Compiler Error Message: CS1061: 'ASP.l_paperset_aspx' does not contain a definition for 'Timer1_Tick' and no extension method 'Timer1_Tick' accepting a first argument of type 'ASP.l_paperset_aspx' could be found (are you missing a using directive or an assembly reference?)

Source Error:


Line 23:                     <contenttemplate>
Line 24:                     
Line 25:                         <asp:Timer ID="Timer1" runat="server" ontick="Timer1_Tick">
Line 26:                         </contenttemplate>
Line 27:                         <asp:Image ID="Image1" runat="server" />