Request for Session time out alert with master page

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C#

ASP.NET

Hai All,
I am using ajaxtoolkit’s modalpopupextender control to alert user about expiring session.what i need for every 5mins if the site is ideal it will show alert message your seesion is expering if u want to extend if it is ok then u have reset the time like that for that
i wrote my code like this.but dnt knw i am getting error in script its not wroking properly can any one tel me how to do this task

<script type="text/javascript">
            function ShowAlert() {
                $find('mpe_alert').show();
            }
            function hide() {
                $find('mpe_alert').hide();
            }
            function onOk() {
                $find('mpe_alert').hide();
                _doPostBack($find('btnOk'), '')
            }

in body tag i worote like this

body>
    <form id="form1" runat="server">
        <%--  <asp:ScriptManager ID="ScriptManager1" runat="server" AsyncPostBackTimeout="180" ScriptMode="Release" EnableScriptGlobalization="true" EnablePageMethods="true" >
    </asp:ScriptManager>--%>
        <telerik:RadScriptManager  runat="server" ID="RadScriptManager1" EnablePageMethods="true" />
        <telerik:RadSkinManager ID="QsfSkinManager"  runat="server" Skin="Metro" ShowChooser="false" />
   <asp:HiddenField ID="hdnSessionExpire" runat="server" />
            <cc1:ModalPopupExtender ID="mpe_alert"  runat="server" TargetControlID="hdnSessionExpire"
                PopupControlID="pnlAlert" CancelControlID="btnCancel" OkControlID="btnOk" BehaviorID="mpe_alert"  önOkScript="onOk()">
            </cc1:ModalPopupExtender>
            <asp:Panel ID="pnlAlert" runat="server" Height="100px"
                Style="display: none" Width="250px">
                <table width="100%">
                    <tr>
                        <td align="left" style="font-weight: bold; font-family: Arial">
                            <asp:Label ID="lblSessionAlert" runat="server" Text="Session Expiry Alert"></asp:Label>
                    </tr>
                </table>
                <table>
                    <tr>
                        <td colspan="2">
                            <asp:Label ID="lblMessage" runat="server" Font-Bold="true" Text="Your session is going to expire in 1 minute. Would you like to extend your session?"></asp:Label>
                        </td>
                    </tr>
                    <tr>
                        <td>
                            <br />
                        </td>
                    </tr>
                    <tr>
                        <td align="right">
                            <asp:Button Text="Yes" value="Yes" runat="server" ID="btnOk" />
                        </td>
                        <td align="left">
                            <asp:Button Text="Cancel" value="No" runat="server" ID="btnCancel" />
                        </td>
                    </tr>
                </table>
            </asp:Panel>

        </div>

and this is my .cs file code

Session.Timeout = 5;
           int MillisecondsTimeout = (Session.Timeout * 60000) - 120000;
           string strScriptAlert = @"window.setInterval('ShowAlert()' , " + MillisecondsTimeout.ToString() + @");   ";
           ScriptManager.RegisterStartupScript(this.Page, this.GetType(), "Alert", strScriptAlert, true);

           int Timeout = (Session.Timeout * 60000) - 60000;
           string strScriptHideAlert = @"window.setInterval('hide()' , " + Timeout.ToString() + @");   ";
           ScriptManager.RegisterStartupScript(this.Page, this.GetType(), "HideAlert", strScriptHideAlert, true);
           Response.AppendHeader("Refresh", Convert.ToString((Session.Timeout * 60)) + ";URL=Login.aspx");