ASP.NET Authorization... Doesn"t support Domain Local Groups?

I have an app that is being deployed and they are trying to use the ASP.NET
Authorization. Problem is that if they use a Domain Local Group then the app
will not let you in even if you are in the group. If you make the
authorization point to a Global group then it lets you in. I've looked and
couldn't find any material about this. Our AD is 2k Mixed mode if that
helps. Anyone have any ideas?