read the thread i linked to a little more carefully.
take a look at your login page. Double click the authenticate user server behavior, and go to the third page. Make note of all of the session varaibles that are set here.
in the code, notice this line:
//store user sessions - create a application variable for each user session variable from the login page
$userID = $_SESSION['userID'];
//add more application variables if you need to
and also notice this line:
//restore the users session variables
$_SESSION['userID'] = $userID;
your sessions may have different names, so those lines of code will need to be adjusted as necessary