With
        jquery-1.4.2.min.js
        jquery-ui-1.8rc3.custom.min.js

A master script using tabs begins

1. <?php
2.     session_start();
3.         ...............($_SESSION variables defined there)
   
4.       <div id="onglets" class="ui-tabs">
5.              <ul>
6.                  <li>
7.                      <?php echo $refer ?>
8.                      <a href='./Tab1.php'></a>
9.                  </li>
10.         .....................

The line 7 is of no sense but just to permit XDebug to stop
The $_SESSION variables initialized before are ok and active at this point

The Tab1.php script begins

1. <?php
2.     session_start();
3.  
   

But at this point (line 3) the $_SESSION array is NULL
It is the same if I dont comment the <session_start() at line 2

What happens with the $_SESSION array ????????