Simplify the Outlook Web App URL, Security issue

Hi there,

I'm following this article ( http://technet.microsoft.com/en-us/library/aa998359(v=exchg.150).aspx ) and I've come to the step where I'm suppose to modify the security settings for the web.config file. The problem is I can't find the group "Authenicated users" , I only have SYSTEM and "Exchnage\Administrators". Am I missing something here?

Stian