Something is preventing your site from properly starting a session.
Proof of that is in not only the error message you initially reported, but also in the fact that if you change currencies via the pulldown menu in the sidebox, it doesn't remember the selection.

Maybe you've fudged the session settings or the server's unable to store session details properly (is your cache folder writable?), or you've got .htaccess redirects set up which are causing confusion by translating something incorrectly, or it's trying to set session cookies using bad domain information ... it could be any number of things, sadly outside the control of Zen Cart itself.


You said you "fixed the admin" ... care to elaborate?