Neither are case sensitive. If it doesn't get passed this, then it might be that your server isn't saving session variables properly. To test this, create two pages.
setSession.php with code:
$_SESSION['test'] = "works";
and viewSession with code:
echo(isset($_SESSION['test'])?$_SESSION['test']:"does not work");
Then browse the setSession.php page with your browser and then go to the viewSession.php page after to see if it works.
Can you put your contact page on a live site and give me FTP access? That would allow me to do some testing and figure out what is wrong on my own.