Hi, first thing to do is check your php.ini, and see what's changed. You did make a backup before you upgraded, didn't you? 😉 Also, usually the main problem with sessions are the register_globals incompatibilities. Check to see if your code uses the $_SESSION['var'] = "value"; method, or the session_register("var"); $var = "value"; method. If it uses the first, you need register globals OFF, if it uses the second, you need register globals ON. I would suggest not turning register globals on, but instead recoding to make it more secure 🙂
Hope that helps,
Matt