PHP 5.3 and Zend Optimizer

There is no Zend Optimizer for PHP 5.3 currently, so php codes encrypted with Zend Guard do not work.

Zend has promised a new version of Zend Optimiser and Zend Guard for PHP 5.3 later this year. But there is a catch, because of compatibility problems apps encrypted with older Zend Guard versions will probably not work with PHP 5.3 .

source: http://forums.zend.com/viewtopic.php?f=57&t=1365