Membership User isn't checking roles properly

I have a custom membership user class
public CustomMembership : MembershiUser, IPrincipal {}
I implement the isInRole method and if I call it
CustomMembership.IsInRole("Administrator") ( return true )
and I have the following web.config for the folder
 
<configuration>
    <system.web>
        <authorization>
            <allow roles="Administrator" />
            <deny users="*" />
            <deny users="?" />
        </authorization>
    </system.web>
</configuration>
 
And I cannot access the folder.
I hav ...