using System;
using System.Diagnostics;
using System.Globalization;
using System.IO;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading;
using System.Web;
 
namespace WebMonitor {
    public class UnhandledExceptionModule: IHttpModule {

        static int _unhandledExceptionCount = 0;

        static string _sourceName = null;
        static object _initLock = new object();
        static bool _initialized = false;

        public void Init(HttpApplication app) {

            // Do this one time for each AppDomain.
            if (!_initialized) {
                lock (_initLock) {
                    if (!_initialized) { 

                        string webenginePath = Path.Combine(RuntimeEnvironment.GetRuntimeDirectory(), "webengine.dll"); 

                        if (!File.Exists(webenginePath)) {
                            throw new Exception(String.Format(CultureInfo.InvariantCulture,
                                                              "Failed to locate webengine.dll at '{0}'.  This module requires .NET Framework 2.0.", 
                                                              webenginePath));
                        } 

                        FileVersionInfo ver = FileVersionInfo.GetVersionInfo(webenginePath);
                        _sourceName = string.Format(CultureInfo.InvariantCulture, "ASP.NET {0}.{1}.{2}.0",
                                                    ver.FileMajorPart, ver.FileMinorPart, ver.FileBuildPart);

                        if (!EventLog.SourceExists(_sourceName)) {
                            throw new Exception(String.Format(CultureInfo.InvariantCulture,
                                                              "There is no EventLog source named '{0}'. This module requires .NET Framework 2.0.", 
                                                              _sourceName));
                        }
 
                        AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(OnUnhandledException);
 
                        _initialized = true;
                    }
                }
            }
        }

        public void Dispose() {
        }

        void OnUnhandledException(object o, UnhandledExceptionEventArgs e) {
            // Let this occur one time for each AppDomain.
            if (Interlocked.Exchange(ref _unhandledExceptionCount, 1) != 0)
                return;

            StringBuilder message = new StringBuilder("\r\n\r\nUnhandledException logged by UnhandledExceptionModule.dll:\r\n\r\nappId=");

            string appId = (string) AppDomain.CurrentDomain.GetData(".appId");
            if (appId != null) {
                message.Append(appId);
            }
            

            Exception currentException = null;
            for (currentException = (Exception)e.ExceptionObject; currentException != null; currentException = currentException.InnerException) {
                message.AppendFormat("\r\n\r\ntype={0}\r\n\r\nmessage={1}\r\n\r\nstack=\r\n{2}\r\n\r\n",
                                     currentException.GetType().FullName, 
                                     currentException.Message,
                                     currentException.StackTrace);
            }           

            EventLog Log = new EventLog();
            Log.Source = _sourceName;
            Log.WriteEntry(message.ToString(), EventLogEntryType.Error);
        }

    }
}

<add name="UnhandledExceptionModule" 
	type="WebMonitor.UnhandledExceptionModule, <strong name>" />