How to fix error ‘This configuration section cannot be used at this path’ when running ASP.NET apps

Problem description:

You receive the error message:

HTTP Error 500.19 - Internal Server Error

This configuration section cannot be used at this path. This happens when the section is locked at a parent level. Locking is either by default (overrideModeDefault="Deny"), or set explicitly by a location tag with overrideMode="Deny" or the legacy allowOverride="false

How to resolve:

1. Make sure ASP.NET is installed, as described here.
2. Unlock the configuration section using the command:

%windir%\system32\inetsrv\appcmd unlock config -section:system.webServer/modules

More Information:

• The new Configuration System in IIS 7