Form Authendication with AD Groups

Hi

I have configured my web.config to use form mode authendication, but with a AD provider. It working great, people can log in with there AD account.

But now i have to built some more secure, because some extra pages have been done, and not all should could locate the new sites.

This example is working

<location path="Default.aspx"><system.web><authorization><allow users="user" /><deny users="*" /></authorization></system.web></location>

This is not working, i think it because it can't look up the users membership or something?

<location path="Default.aspx"><system.web><authorization><allow roles="domain\group" /><deny users="*" /></authorization></system.web></location>