Zen Cart 1.3.9h
Server OS: Linux 3.0.9-nx
Database: MySQL 5.0.91-log
HTTP Server: Apache/2
PHP Version: 5.2.17 (Zend: 2.2.0)
PHP Memory Limit: 128M PHP Safe Mode: Off
PHP File Uploads: On
Max Size: 10M POST Max Size: 8M
Database Data Size: 2,641 kB
Database Index Size: 1,005 kB

Admin and cart seem fine, can logon the select items. At checkout (index.php?main_page=shopping_cart) clicking the "Checkout" button takes me to index.php?main_page=checkout_shipping and a blank screen with a "0" in the upper LH corner.

The config Admin and Cart files were checked and they seem to be pointing to the correct database. There is no problem with the Admin side of the store, can see all the data etc.

The error logs report the follow;
Failed loading /usr/local/lib/ioncube/ioncube_loader_lin_5.1.so: /usr/local/lib/ioncube/ioncube_loader_lin_5.1.so: undefined symbol: zend_unmangle_property_name_ex

20110302T235213: **/index.php
Failed loading /usr/local/lib/ioncube/ioncube_loader_lin_5.1.so: /usr/local/lib/ioncube/ioncube_loader_lin_5.1.so: undefined symbol: zend_unmangle_property_name_ex

20110302T235752: **/index.php
Failed loading /usr/local/lib/ioncube/ioncube_loader_lin_5.1.so: /usr/local/lib/ioncube/ioncube_loader_lin_5.1.so: undefined symbol: zend_unmangle_property_name_ex

What should I be looking for?