PHP Warning: session_destroy

Hi, To stop bots from accessing secured pages, I've added the following code to a banner page that is called by every page. Furthermore, each page starts with <?php session_start(); ?> and includes the banner page: 'top1.php' [banner page] <?php if((eregi("((Yahoo! Slurp|Yahoo! Slurp China|.NET CLR|Googlebot/2.1| Gigabot/2.0|Accoona-AI-Agent))",$_SERVER['HTTP_USER_AGENT']))) { if ($_SERVER['HTTPS'] == "on") { session_destroy(); header("Location: http://localhost/logout.php"); } } ?> I'm testing on localhost with the browser set to 'Googlebot/2.1' - and the code works great. Any page that is set for https is not served, and if https has been set by a previous visit, it goes to http://somepage. However, checking the live version, I get an secure-error_log entry: "PHP Warning: session_destroy() [<a href='function.session-destroy'>function.session-destroy</a>]: Trying to destroy uninitialized session" Question is: didn't the session_start(); on the calling page take effect, or is this some other problem? Is there something like 'isset' to check whether 'session_destroy(); is needed? [I've tried isset, it barfs the code.] Tia, Andre