This is a problem with the PHP installation, possibly some installed php mod is not up to date. This is not an issue with Neos but rather with your hoster.
Sorry for German, but this describes the problem on df:
Open a support ticket with the error to your hoster, they shoudl solve it. Generally it’s quite strange because “Zend Optimizer” is integrated in Zend Engine since PHP 5.3 so this Zend Optimizer stand alone must be really old.