Error 500.19 when Accessing the App Portal Site

[#1]

Summary

When attempting to access the App Portal Site, HTTP Error 500.19 is encountered

Symptoms

When attempting to access the App Portal Site, the following error may be displayed in the browser:

Cause

The Windows Authentication section is locked for the Default Web Site

Resolution

To unlock Windows Authentication at the Default Web Site level,
1. Using IIS manager, select Default Web Site under the Sites view
2. Under the Management section, select Configuration Editor
3. In the Section field, select System.WebServer/Security/authentication/WindowsAuthentication
4. Select "Unlock Section"

[K_Ritter]

This did not resolve my error. The section was already unlocked, but still get the error. Detailed error code is 0x80070021 - Lock violation. It is referencing the web.config file.