Rolegroup doen not seem to work

I have a website which allow users to logon using credentials (Forms-authentication ). This works perfect!
Now I want to update to Windows-authentication, but it does not seem to work: 
The server is Windows Server 2003 SP, IIS version is 6.0 . The relevant section in the web.config looks like: 
<authentication mode = "Windows" /> <authorization> <deny users ="?"/> </authorization> <identity impersonate = "true"/>

In the aspx-file I want to show a number of links, based on the AD-roles:


When I start the webpage, I can see that I am logged on correctly ( domain\user is shown), but there is no link shown.

What am I doing wrong ??