Session problems

Hi there, I'm having some problems using some session commands. This worked on another machine, but for some reason, when I transferred all the files onto a new machine, it wouldn't work anymore. However, it's the exact same code. Anyway, my problem is this: my session variable values aren't being retained. I have a variable $username. When I go clicking around and set $username, it's set (I can print() it out and it's the value I set it to). I declare it as a session variable using session_start(); and session_register(username);. Then I go clicking to the next page, and the variable is no longer set (it's value is nothing), even though there is a session_start(), which should make $username accessible (and unchangeable if the php.net pages are correct). Now, I think I may know the problem: The page I go to includes the page that has the session_start() command, which runs a function that checks the value of my session variables. So I'm asking for a variable two stack calls (is that the proper terminology?) after my script page, and one stack call after my session_start() call (but my print() statement says that $username is unset right after the call to session_start()). But I thought session variables were completely global, accessible from any page in any function. Does this mean that, on this new machine, a setting is set so that session variables aren't global? Is there another problem I don't know about? Can anyone help please? Liam Gibbs