Ben H Blog - Keep it Simple, Then Refactor.

I recently deployed a solution I was working on that used ASP.NET Authentication via the WCF Authentication Service.  When I called the service it returned a fault exception that read:

AuthenticationService is Disabled

I could not figure out why.  What happened was my web.config on the server was lacking the following entry to enable the service:

<system.web.extensions>
  <scripting>
    <webServices>
      <authenticationService enabled="true"/> 
    </webServices>  
  </scripting> 
</system.web.extensions>

I hope this helps solve your problem.