Help on protect sub-directories with roles

[Luca]

I am trying to protect sub-directories making use of the web.config
<location>-tag.
Additionally I would like to make us of my internal roles instead of the
user(names). I.e.:

<location path="web/admin">
<authorization>
<allow roles="Super Administrators"/>
<deny users="?"/>
<authorization>
</location>

This does NOT seem to work! On the other hand

<location path="web/admin">
<authorization>
<allow roles="sa"/>
<deny users="?"/>
<authorization>
</location>

does work.
I would have expected that in the former case the IPrincipal>>IsInRole
method is called, but this is not the case.

Can anybody enlighten me on how to make rolebased authorization, or am I
trying to do soemthing impossible.

thx all!