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error handling on my website

I am using .net framework 4.0 with c#.
I want to auto redirect to a page when any uncaught exception occurs on my web pages.
I introduced an error in the key name on the web.config file to test this functionality.

When I run this in the debugger I get the following error:
"ArgumentNullException was unhandled by user code"

on the following line: throw (new ArgumentNullException());        
Please review the following and suggest corrections.


I added this code to my web.config:
    <compilation debug="true" targetFramework="4.0"/>
    <customErrors defaultRedirect="PageEvent.aspx" mode="On">

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Then I added a web form named PageEvent.aspx to my website.

The PageEvent.aspx has the following code:
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="PageEvent.aspx.cs" Inherits="PageEvent" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <form id="form1" runat="server">
    <div class = "Error">
        <asp:Label ID="Label1" runat="server" Text="Error Caught in Page_Error event."></asp:Label>
        <asp:Label ID="_ErrIn" runat="server"></asp:Label>
        <asp:Label ID="_ErrMessage" runat="server"></asp:Label>
        <asp:Label ID="_StackTrace" runat="server"></asp:Label>

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The PageEvent.aspx.cs has the following code:

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

public partial class PageEvent : System.Web.UI.Page
    protected void Page_Load(object sender, EventArgs e)
        throw (new ArgumentNullException());        

    public void Page_Error(object sender, EventArgs e)
        Exception objErr = Server.GetLastError().GetBaseException();
        string ErrIN = "Error in: " + Request.Url.ToString();
        string ErrMessage = "Error Message: " + objErr.Message.ToString();
        string StackTrc = "Stack Trace: " + objErr.StackTrace.ToString();
        //show error on screen
        _ErrIn.Text = Session["ErrIn"].ToString();
        _ErrMessage.Text = Session["ErrMessage"].ToString();
        _StackTrace.Text = Session["StackTrc"].ToString(); 


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1 Solution
Miguel OzSoftware EngineerCommented:
and follow  the steps described at: "How to use the Web.config file"
the problem of your page is that we do not use page_error to surface the exception. just use page_load
protected void Page_Load(object sender, EventArgs e)
        Exception objErr = Server.GetLastError().GetBaseException();
//fill up your labels here

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