'Zen Cart™ can work with the "Register Globals" setting on or off. However, having it "off" leaves your system somewhat more secure.
If you wish to disable it, and your hosting company won't turn it off for you, you might try adding this to an .htaccess file in the root of your shop (you may have to create the file if you don't already have one):
php_value session.use_trans_sid off
php_value register_globals off
#php_value register_globals off
<Files ".ht*">
deny from all
</Files>
or talk to your hosting company for assistance.'