Knowledgebase

If you want to use a custom error page in ASP .NET and want to show the exception details on that page, you must save the Server.GetLastError to a sessions variable in the Global.asax Application_Error event, manually clear the error and than manually redirect to a ErrorPage.aspx and do not use the Web.config “customErrors” tag.

Global.asax

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.SessionState;

namespace CustomBeheer
{
    public class Global : System.Web.HttpApplication
    {
        /// <summary>
        /// Code that runs when an unhandled error occurs
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        void Application_Error(object sender, EventArgs e)
        {
            // Catch exception and save to session variable, for displaying in ErrorPage.aspx
            Exception ex = Server.GetLastError();
            try
            {
                // Session object is not always available, so use try finally block.
                // This will prevent recursive loop.
                Session["EncounteredException"] = ex;
            }
            finally
            {
                // To use the Session variable in ErrorPage.aspx we must clear the error and then manualy redirect to the ErrorPage.aspx.
                // Because we manualy redirect, we don't use the "customErrors" tag in the Web.config
                Server.ClearError();
                Response.Redirect("ErrorPage.aspx");
            }
        }
    }
}

ErrorPage.aspx

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

namespace Beheer
{
    public partial class ErrorPage : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            //Exception ex = Server.GetLastError();
            this.ShowError();
        }
        private void ShowError()
        {
            Exception encounteredException = Session["EncounteredException"] as Exception;

            if (encounteredException != null)
            {
                Session["EncounteredException"] = null;
                lblError.Text = encounteredException.ToString();
            }
        }
    }
}

[No changes to the Web.config]

Result

The text: “Oops… something bad happened” is a predefined text and the “System.Web.HttpUnhandledException…” shows the exception details, catched in the global.asax Application_Error event.

More on CustomErrorPages

http://aspnetresources.com/articles/CustomErrorPages.aspx