Umbraco version 4.1, asp.net 3.5, window 2008 iis 7.5

I'm trying to implement a single sign on implementation to get a single sign-on point and member database for several umbraco sites we will be hosting on different domains.

I have a demo solution working outside umbraco. I'm now trying to implement it in umbraco and have thus enabled forms authentication and the asp.net sqlmembership provider and placed a custom login page (aspx). I can now logon using the the new login page and the loginstatus control text on it changes to logoff (a sure sign logon was successfull). A test page (aspx) with the same control deployed to different umbraco folders works fine. But when I put the loginstatus control inside a umbraco template it just keeps displaying the login text.

Placing this <%= Context.User.Identity.IsAuthenticated.ToString() %> in a template gives me an error because the user object is null. Does anyone know why this is happening? Non umbraco pages work fine so what is it, that is different about the umbraco templates?