I've spent a lot of hours these last two days trying to install Zend Optimizer on a Linux server (x64-64) with Apache 2.2 using the worker MPM mode. The actual installed PHP version on this server is 5.2.11.
After downloading the newest Zend Optimizer (version 3.3.9) from www.zend.com, you may follow the installation doc but it won't work. So I found hints that Zend Optimizer isn't compatible with
a) the Apache2 worker and
b) PHP version higher than 5.2.9.
Those hints only affect Zend Optimizer versions below 3.3 though, so it should have worked with 3.3.9.
However, after not receiving any answers in the Zend support forum I continued my research. I've tried it with a way older version (3.2.6) but here I got the problems with the worker module. With a little trick I was able to download the version 3.3.0 from the Zend website (hidden download) and what a surprise: This version works!
Summary: If you want to install and use Zend Optimizer on your Apache 2.2 webserver (with MPM worker) and PHP 5.2.11 you currently have to use Zend Optimizer version 3.3.0 (not the newest one!)