500.21 Internal Server Error after installing Geocortex Essentials

Overview:

The .NET Framework 4 can be installed side-by-side with previous versions of the .NET Framework on a single computer. If IIS was previously enabled on the computer, the setup process for the .NET Framework automatically registers ASP.NET 4 with IIS. However, if you install the .NET Framework 4 before you enable IIS, you must run the ASP.NET IIS Registration tool in order to register the .NET Framework with IIS and create application pools that use the .NET Framework 4.

http://msdn.microsoft.com/en-us/library/vstudio/k6h9cz8h%28v=vs.100%29.aspx

Solution:

To resolve, run the following command in a command prompt window:
 

C:\Windows\Microsoft.NET\Framework64\v4.0.30319 > aspnet_regiis -i

This issue may also manifest itself as a 500 error.  The following exception will be logged in the Windows Application Event Log:  
 

?Exception type: ConfigurationErrorsException Exception message: Could not load type 'System.ServiceModel.Activation.HttpModule' from assembly 'System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'. at System.Web.Configuration.ConfigUtil.GetType(String typeName, String propertyName, ConfigurationElement configElement, XmlNode node, Boolean checkAptcaBit, Boolean ignoreCase)