Just because a page has a .aspx extension, does not mean that it will start up a session.
I encountered this because I installed an asp.net version of the user tracking code at TODCon. I was at a loss when all the sessions in the database had http://www.todcon.org/ as the referer.
I found that even though it was an asp.net site, the index page did not have any code on it, so a session was not started until they navigated to another page with code on it.
just thought you should know.