Some configuration sections are only allowed in the "root" of the application, and then authentication
is one of them.
You need to configure IIS to run your site as an application, not a subdirectory in an existing application.
For IIS 7+, right-click the directory containing your web application and select Convert To Application.
EDIT
Ari van Someren is right. Having carefully studied your error, you want the <authentication>
configuration to be up one level in web.config, and not in web.config in the views.
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