Configure Web.Config in order to use asp:ScriptManager
File: Default.aspx <%@ Page Language="C#" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <script runat="server"> protected void btnSubmit_Click(object sender, EventArgs e) { throw new Exception("Server Error"); } </script> <html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server"> <title>UpdatePanel Error</title> </head> <body> <form id="form1" runat="server"> <asp:ScriptManager id="sm1" Runat="server" /> <asp:UpdatePanel id="up1" runat="server"> <ContentTemplate> <asp:Button id="btnSubmit" Text="Submit" OnClick="btnSubmit_Click" Runat="server" /> </ContentTemplate> </asp:UpdatePanel> </form> </body> </html> Web.Config <configuration> <system.web> <customErrors mode="Off"/> <compilation debug="true"/> <pages> <controls> <add tagPrefix="asp" namespace="System.Web.UI" assembly="System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" /> </controls> </pages> </system.web> </configuration>