Forms authentication forces re log in for subfolders?!?

I have a web application were I seperating the pages into subfolders and only want the user to log in at the main page and then they can click links to go to differant pages (which are in subfolders). Well once the user is authenticated and they can click a link to go to a page which resides in a subfolder of the application, it goes back to the LogInURL where they can log in again and get to the requested page. I know theremust be a way to keep the authentication valid for pages in the main folder and its subfolders. Any help is very appreciated.