Handler "ExtensionlessUrlHandler-Integrated-4.0" has a bad module "ManagedPipelineHandler" in its module list

Question

Try to re-register ASP.NET with aspnet_regiis -i. It worked for me.

A likely path for .NET 4 (from elevated command prompt):

c:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet_regiis.exe -i

http://forums.iis.net/p/1190643/2026401.aspx

If you're running into this error with Windows 8/Windows Server 2012 and .Net 4.5 follow these instructions here: http://www.britishdeveloper.co.uk/2013/01/handler-extensionlessurlhandler.html

Go to "turn Windows features on or off" Then Internet Information Services Then World Wide Web Services Then Application Development Features And then enable ASP.NET 4.5

This worked for me (although the wizard and wording is a little different in Windows Server 2012, but you'll figure it out). With this being said, why this is necessary after installing everything through the Web Platform Installer including all of the dependencies is completely beyond me...

Despite following most of the advice on this page, I was still getting problems on Windows Server 2012. Installing .NET Extensibility 4.5 solved it for me:

Add Roles and Features > Server Roles > Web Server (IIS) > Web Server > Application Development > .NET Extensibility 4.5

For Windows 10 / Windows Server 2016 use the following command:

dism /online /enable-feature /featurename:IIS-ASPNET45 /all

The suggested answers with aspnet_regiis doesn't work on Windows 10 (Creators Update and later) or Windows Server 2016:

C:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet_regiis.exe -i
Microsoft (R) ASP.NET RegIIS version 4.0.30319.0
Administration utility to install and uninstall ASP.NET on the local machine.
Copyright (C) Microsoft Corporation. All rights reserved.
Start installing ASP.NET (4.0.30319.0).
This option is not supported on this version of the operating system. Administrators should instead install/uninstall ASP.NET 4.5 with IIS8 using the "Turn Windows Features On/Off" dialog, the Server Manager management tool, or the dism.exe command line tool. For more details please see http://go.microsoft.com/fwlink/?LinkID=216771.
Finished installing ASP.NET (4.0.30319.0).

Interestingly, the "Turn Windows Features On/Off" dialog didn't allow me to untick .NET nor ASP.NET 4.6, and only the above DISM command worked. Not sure whether the featurename is correct, but it worked for me.

Run one of these commands :

For 32 Bit Windows OS:

c:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet_regiis.exe -i

For 64 Bit Windows OS:

c:\Windows\Microsoft.NET\Framework64\v4.0.30319\aspnet_regiis.exe -I

This https://stackoverflow.com/a/13266763/1277458 works perfectly. But if you have 64-bit operation system use Framework64 instead of Framework in path:

c:\Windows\Microsoft.NET\Framework64\v4.0.30319\aspnet_regiis.exe -i

The problem

You are using SimpleWorkerRequest in a scenario that it wasn't designed for. You are using it inside of IIS. If you look at the prior MSDN link (emphasis is mine):

Provides a simple implementation of the HttpWorkerRequest abstract class that can be used to host ASP.NET applications outside an Internet Information Services (IIS) application. You can employ SimpleWorkerRequest directly or extend it.

Also, if you look at the MSDN documentation for the System.Web.Hosting namespace (SimpleWorkerRequest is in this namespace), you will also see something similar to the above (again, emphasis is mine):

The System.Web.Hosting namespace provides the functionality for hosting ASP.NET applications from managed applications outside Microsoft Internet Information Services (IIS).

The solution

I would recommend removing the call to SimpleWorkerRequest. Instead, you can use a Microsoft solution to make sure your web site automatically starts up after it recycles. What you need is the Microsoft Application Initialization Module for IIS 7.5. It is not complicated to configure, but you need to understand the exact options. This is why I would also recommend the Application Initialization UI for IIS 7.5. The UI is written by an MSDN blogger.

So what exactly does the Microsoft solution do? It does what you are trying to do - IIS sends a "get" request to your website after the application pool is started.