Actually AndyReed is CORRECT.
After I upgraded two of my servers to the latest version php 5.2.10 and zend optimizer 3.3.3 the zend encoded script did not work. I contacted the company that wrote the script for me to find out how to make this work. This company contacted Zend and was told that Zend 3.3.3 is not compatible with php5.2.10. Here is a link to the announcement made by the Zend Product Manager about this incompatibility issue:
Zend Forums • View topic - Problems with PHP 5.2.10 and Zend Optimizer
If I got paid for every time a software author made the same mistake as general users using their programs who more than often incorrectly thought their programs weren't compatible with a new release of something only to find out later that wasn't the case at all, I'd be a multi-billionaire by now!
When PHP 5 was first released a number of years ago, I got into arguments with hundreds of software authors who absolutely swore their programs would not work with PHP5 and the new PHP 5 was causing incompatibilities. To their dismay (and often embarrassment), I showed each of them that in nearly every case with very few exceptions, all their programs actually worked 100% perfectly with PHP5 with no problems whatsoever and without the need for any patches or modifications! It turned out that the problem at the time was not PHP5 but rather how people were installing it. As many hosts were reluctant to make the jump directly to PHP5, many kept both PHP4 and PHP5 which is actually what caused their troubles and once that was revealed, no more problems. It was much the same when Apache 2 was released. MySQL 5 as well although MySQL 5 really did have some compatibility issues to address. The point I am making it is not uncommon for not only regular users but software authors not to know their own products well enough to know if an issue is really an incompatibility or not and like many users quickly make wrong assumptions.
In the case of PHP 5.2.10, we have extensively tested that version independently and have thrown plenty of scripts at it both commercially available as well as ones by our own design testing very nearly every function available to PHP 5 both Zend encoded and regular as well as Ioncube encoded and a few others and we have noted no significant issues with any of them with PHP 5.2.10.
We have however confirmed substantial issues with PHP 5.3.0.
The above would lead us to suspect anyone thinking there is a problem with PHP 5.2.10 in terms of compability issues with Zend may have some other issue going on with their servers beyond simply upgrading their PHP version. Even a slight change in configuration options or system libraries could have an impact that you might miss and not realize there were a 3rd party factor going on outside what you thought was "just an upgrade".
Bottom line though is PHP 5.2.10 does in fact work with Zend Optimizer 3.3.3 and from what we can tell works well without any significant issues. The only variances we found were in a few very rare obscure functions not likely to be found in any normal average program. Unless you are doing something very, very specialized, you are not likely to run into any of those few items and certainly not with any normal commercially available program out there.