Multiple user session management confusion?

Dear All We are testing a multi-user quiz system with PHP session management. Everything has been fine until we tested the system with about 12 users... Each user gets an individual instantiation of some questions and they type in some answers and submit them for marking. To remember the question instantiations across script invocations we store them in a $_SESSION variable (nb. I don't use session_register or similar, I just set $_SESSION['var'] directly). Upon submission we log the questions, the correct answers (all from the $_SESSION variable), and the user answers (from $_POST) in a database for marking later. Everything seemed to work fine, except... One user is absolutely sure that the question instantiations logged in the database are NOT the ones he saw on his browser! I've reviewed the code paths and I am also sure (!) that the questions cannot be re-instantiated across script invocations. So that leaves me looking for another reason. Could the session management in PHP have gotten confused and he got someone elses SESSION variable?? Is this possible ? Or am I being naive and should look harder at my code? Setup is: Server: RedHat 7.3 Apache 1.3.26 PHP 4.2.2 MySQL 3.23.52 Client: Win2000 Professional 5.00 SP2 Internet Explorer 6.0.2600 Any tips gratefully received! Thanks Ian -- Ian Thurlbeck http://www.stams.strath.ac.uk/ Statistics and Modelling Science, University of Strathclyde Livingstone Tower, 26 Richmond Street, Glasgow, UK, G1 1XH Tel: +44 (0)141 548 3667 Fax: +44 (0)141 552 2079