Thank you John. I have tried that file now, but it returns a similar error,

"Fatal error: The file /xxxxx/xxxxx/public_html/includes/classes/rlNavigator.class.php was encoded by the ionCube Encoder for PHP 5 and cannot run under PHP 5.5. Please ask the provider of the script to provide a version encoded with the ionCube Encoder for either PHP 5.3 or PHP 5.4 or PHP 5.5. in Unknown on line 0"

Is the cause of this the ZEND Guard you speak of or was it the wrong file?