if we have error message this in asp.net when we make new .aspx we must add this below:
<asp:ScriptManager ID="ScriptManager1" runat="server" />
or
<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server" />
example file default.aspx
<%@ Page Title="" Language="C#" MasterPageFile="~/cr.Master" AutoEventWireup="true"
CodeFile="AllPengeluaran.aspx.cs" MaintainScrollPositionOnPostback="true" Inherits="Pengeluaran_ALL_AllPengeluaran" %>
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="CntnPlaceBreadcrumb" runat="server">
</asp:Content>
<asp:Content ID="Content3" ContentPlaceHolderID="CntnPlaceMain" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server" />
<asp:Panel ID="pnlPengeluaranAll" runat="server">
<fieldset>
<table>
<tr>
<td>
TANGGAL TRANSAKSI
</td>
<td>
:
</td>
<td>
<asp:TextBox ID="txtInputTanggall" runat="server" border-color="darkgreen"></asp:TextBox>
</td>
<td>
<asp:ImageButton ID="ImageButton1" runat="server" ImageUrl="~/images/calendar.gif" />
</td>
<td>
<asp:CalendarExtender ID="cldpilihtanggalAll" Enabled="true" Animated="true" runat="server"
TargetControlID="txtInputTanggall" PopupButtonID="ImageButton1">
</asp:CalendarExtender>
</td>
</tr>
</table>
</fieldset>
</asp:Panel>
</asp:Content>