The problem is due to Plesk 8.4 (what you server is running). By default, Plesk 8.4 installs the ionCube loader. While ionCube and Zend can run on the same machine, they have to be loaded in a certain order. Otherwise, Zend encoded files will not work. The easiest way to resolve the problem is to open your php.ini file, copy the lines for Zend into a new file and remove them from the php.ini file. Save the php.ini file. Then, save your new file that contains the Zend lines as "zend.ini" and place it into your /etc/php.d directory. Once you do that, restart Apache.