Most Cpanel/WHM servers come with PHP and Zend installed. With the recent (and important) update of PHP 5.2.1, the Zend Optimizer that is installed by default (version 3.0.1 as of this writing) breaks.

You might begin to see a message like this:

To fix this, simply login to your SSH as root and execute the following command to upgrade Zend Optimiser:

/scripts/installzendopt 3.2.8

Note that if you skip the version number, Zend Optimizer 3.0.1 will be installed by default. The trick is to specify the version as above. This will also work in the future, so as long as you know the latest released version of Zend Optimizer, just replace the red text above with that number.