If you have register_globals enabled in your PHP installation still, then you will have major problems if you are loading the TinyMCE rich text editor. I am attempting to find a work-around for this, but it's not going to be an immediate fix. Please disable register_globals in your servers php.ini file or talk to your web-hosting provider about this today. PHP should not be running with register_globals on.
If you need to disable it, you can create a .htaccess file and place it in your ListMessenger application directory with the following code in it:
php_value register_globals 0
For more information on why register_globals is *terrible*, please see php.net: http://www.php.net/register_globals