are you sure that is the correct session name?
try dumping the session to make sure you have the right session name:
<?php @session_start(); var_dump($_SESSION); ?>
you may need to add session_start(); and session_commit(); after resetting the session:
// reset the userID session var
@session_start();
$_SESSION['SecurityAssist_MEMID'] = $userID;
session_commit();