role-based security and ActiveDirectory groups

hello,

im having a little problem w/ role-based security and ActiveDirectory (AD), hoping someone can help. im trying to restrict access to my app to only users within a particular AD group. details:

- ASP.NET 3.5 intranet app; Visual Studio 2008

- deployed to a Windows Server 2008 (IIS7) machine

- uses Windows authentication

- all desired domain users reside in a custom AD group, "FOO_BAR".

- requesting the User.Identity.Name yields: "OURDOMAIN\SomeUserName"

- requesting all group membership yields:

     Everyone
     OURDOMAIN\Domain Users
     OURDOMAIN\FOO_BAR

...all looks good. so the problem? when i request:

   User.IsInRole(@"OURDOMAIN\FOO_BAR") or
   User.IsInRole("FOO_BAR") or

...i get False< ...