Zend is no longer supported with out upgrade to PHP 5.3 as it was discontinued in this version. Some people have reported using different solutions such as IonCube, which is compatible with PHP 5.3 and supported on our servers. As Zend Optimizer code won’t run in PHP 5.3, and we can’t downgrade our servers to a previous and less-secure version of PHP, you would be limited to two options:
1) You can recompile the site code using a different encoder such as IonCube or,
2) You can choose to not encode PHP and use the pure source.