Server.Transfer issue

I have a have an issue with Server.Transfer I use it in a secure page - this is my security not HTTPS On page load the first thing I call is my method to authenticate user Authenticate user - test session state and if the user is not authenticated sends the user to a login page. Previously this was done via response.redirect and worked ok. I now use Server.Transfer as a direct replacement, howver it doesn't seem to work. Although I see no errors, the page does not transfer, nor does it contain a reference to it's style list. This page uses a master page. Any ideas what might be causing it? Thanks in advance. John ...