SslNegotiateCert Web.Config Error with Thinktecture.IdentityServer .NET 4.5
===

I am using the Thinktecture.IdentityServer (OnPremise) .NET 4.5 version. I need some assistance debugging a configuration issue. When I try to access my OAuth endpoint, I get a 

> "HTTP Error 500.19 - Internal Server Error The requested page cannot
> be accessed because the related configuration data for the page is
> invalid."

This is the Config 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".

The Config Source for the problem area in the web.config is:

    34:       <security>
    35:         <access sslFlags="SslNegotiateCert" />
    36:       </security>

I am uncertain how to move forward. I tried this solution: http://blog.thinkoriginally.com/2010/02/17/asp-net-config-error-this-configuration-section-cannot-be-used-at-this-path/ but no success