SCCM 2012 PORTALWEB is not responding to HTTP requests

After installing the Application Catalog in Config Manager 2012 on Windows Server 2008 R2 it is common to see the following error in SMS_PORTALWEB_CONTROL_MANAGER:

Portal Web Site Control Manager detected PORTALWEB is not responding to HTTP requests.  The http status code and text is 500, Internal Server Error.
Possible cause: Internet Information Services (IIS) isn't configured to listen on the ports over which PORTALWEB is configured to communicate.
Solution: Verify that the designated Web Site is configured to use the same ports which PORTALWEB is configured to use.
Possible cause: The designated Web Site is disabled in IIS.
Solution: Verify that the designated Web Site is enabled, and functioning properly.
For more information, refer to Microsoft Knowledge Base.

This issue occurs because the Applicationhost.config file for Windows Process Activation Service (WAS) has the following section defined, and this section is incompatible with the .NET Framework 4.0.

<add name="ServiceModel" type="System.ServiceModel.Activation.HttpModule, System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" preCondition="managedHandler" />
This section should be defined as follows:
<add name="ServiceModel" type="System.ServiceModel.Activation.HttpModule, System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" preCondition="managedHandler,runtimeVersionv2.0" />

Note: You can find the Applicationhost.config file in the following location:

%windir%\system32\inetsrv\config

To resolve this issue ASP.NET needs to be registered with .NET Framework 4.0.:

1. Navigate to the following path:
%windir%\Microsoft.NET\Framework\v4.0.30319 (x86 Windows)
OR
%windir%\Microsoft.NET\Framework64\v4.0.30319 (x64 Windows)

2. Run "aspnet_regiis.exe" /iru

Viola! Keep an eye on status manager over the next hour and you will see that this error message will disappear.