the code looks correct this time, there are 2 possibilities:
1) a php error is occurring on the page:
add the following code at line 1 to turn error reporting on:
<?php
error_reporting(E_ALL);
ini_set('display_errors','on');
?>
2) The server is not storing session variables properly, use the sessionTest page from the following thread to test the servers session management:
showpost.php?p=23826&postcount=2
also, try adding the following code just before the </body> tag on the contact page:
<pre><?php var_dump($_SESSION); ?></pre>