I’ve been contacted recently by a number of Zen Cart users who are experiencing on occasion, an error similar to the following while working in the administrative section of their sites.
Catchable fatal error: Object of class queryFactoryResult could not be converted to string in … html_output.php
The problem you are experiencing stems from leftover legacy code that is incompatible with PHP5.
Here are two links that will help you understand and correct the issue.
http://www.zen-cart.com/forum/showthread.php?t=90739
http://www.zen-cart.com/forum/showpost.php?p=487734&postcount=11
An interim workaround has been provided by the Zen Cart team. The link to the files which solve this issue are provided here.
http://www.zen-cart.com/forum/showpost.php?p=487360&postcount=10