Fix IIS Error: HTTP Error 500.19 - Internal Server Error

Problem

When running a web application, we got:

Reason

IIS allows server administrators to prevent users from overriding specific configuration directives in a user-defined web.config file. This is similar to the AllowOverride directive in Apache. The error states that a configuration directive used in our suggested web.config file cannot be overridden.

Resolution

1. Open %SystemRoot%\System32\inetsrv\config\applicationHost.config
2. Search for the statements below and change the allowOverride attribute from Deny to Allow

3. <section name="handlers" allowOverride="Deny" />
   <section name="modules" allowOverride="Deny" />

   Restart IIS

Besides this, we may have eazy fixes whthout knowing the reason.

Fix 1

A lazy fix by myself, just installing the whole components for IIS, by

• Control Panel
• Programs
• Programs and Features
• Turn Windows Feature on or off

Or, 

• Click the "Start button"
• lIn the search box, enter "Turn windows features on or off".

such as:

it works.

Fix 2

Somebody suggested we do not need to install the whole components of IIS; just need to install the "Application Development Features" except CGI. It works too.

or:

Fix 3

Somebody suggested:

I was missing the .NET 4.x integration in IIS. then I just choose:

• Application Development Features => ASP.NET 4.X

I have never tried this solution, but you may try it. 

References

• Telerik RadControls HTTP Error 500.19 Config Error This configuration section cannot be used at this path
• Error Code_ 0x80070021 (microsoft.com)
• Troubleshoot IIS Configuration Option Cannot Be Used - SupportPal Documentation