From the Zen Cart Support Forum yesterday:
PHP 5.3 was released a few months ago, and along with it come many problems due to the PHP authors’ decisions to backport many PHP 6 features into 5.3 and deprecate several oft-required functions. In so doing, they broke many things affecting Zen Cart operation in v1.3.8a and older.
A patch is now available for use by those whose hosts have upgraded (or have announced imminent plans to upgrade) to PHP 5.3.
This patch is ONLY needed if you are attempting to run Zen Cart v1.3.8 on a server which is using PHP 5.3.
(This patch IS compatible with older versions of PHP, so is safe to install if you’re using PHP 4.x or 5.2.x.)
THIS PATCH IS **NOT** COMPATIBLE WITH PRIOR VERSIONS OF ZEN CART.
THE ATTACHED ZIP IS ONLY SUITABLE FOR v1.3.8 / v1.3.8a sites.
The Announcement (and patch) is available from http://www.zen-cart.com/forum/showthread.php?t=140960.
All Zen Cart store owners are encouraged to subscribe to the Announcement thread of the Zen Cart Support forum to receive announcements via email.

