Restricted access to sub-folder in iis6 doesn't work?

Basically I'm trying to add restriction to sub-folder (which contains pdf) in web.config for iis6 as below.
It doesn't work at all.

       <system.web>    
             <authentication mode="Forms">
            <forms name=".Admin" loginUrl="~/Admin/logon.aspx"/>
        </authentication>
        </system.web>
       <location path="Admin">
        <system.web>
            <customErrors mode="Off" />
            <pages theme="Admin" />
     ...