HTTP Error 500.19 - Internal Server Error

Description: The requested page cannot be accessed because the related configuration data for the page is invalid. 

Error Code: 0x80070021 

Notification: BeginRequest 

Module: IIS Web Core

This may happen when .NET is installed before the site was installed on IIS

locate the appropriate under C:\Windows\Microsoft.NET

Open command prompt and run the command:

aspnet_regiis -i

Restart IIS with

iisreset /noforce

The .NET pages should work now.