Can't attach audio samples to products

I've been trying to add audio samples to my Product - Music type product(s). (Since my audio products aren't music, I renamed Product - Music to Product - Audio.) I can create the Media Type and create the Media Collection, but when I try to assign the Media Collection to the Product, Zen Cart pauses for a moment, then changes to the Admin Home Page. The Media Collection has not been attached to the Product. The product in question (although I intend to do this with all my products) is Historic Concord California Walking Tour.

BayAreaGuidedWalks.com/zencart/

Zen Cart v1.3.9h new installation
Website Source hosting company
Linux 2.6.18-274.3.1.el5
PHP ver: 5.2.14 (Zend: 2.2.0)
Database: MySQL 5.0.77-log
HTTP server: Apache