I've updated from 9.10 to 10.04, but unfortunately the PHP provided with 10.04 is not yet supported by zend optimizer.
As far as I understand, I need to somehow replace the PHP 5.3 package provided under 10.04 with an older PHP 5.2 package provided under 9.10. However I'm not sure whether this is the right way to downgrade PHP and if yes, I don't know how to replace the 10.04 package with 9.10 package.
Could you please help me with that?
This thread will tell you exactly how to downgrade PHP from 5.3 to 5.2 in Ubuntu 10.04:
http://ubuntuforums.org/archive/index.php/t-1447401.html
Update: the OP commented below that the following script found here solved his issue.
This post tell you how to install php from "karmic" repository: http://mrkandy.wordpress.com/2010/04/16/install-php-5-2-x-in-ubuntu-10-04-lucid/
Steps: