So we’re doing a big change to improve PHP on our platform, however I ran into a problem when trying to setup and use Zend Server CE 5.2.17. It appears it works great if you use Network Service, but because we want our platform to be more secure, we are running each Application Pool as a unique user. I have a personal Virtual server and just happened to have Zend Server CE 5.2.13, it works exactly the same way and does not have the problem!
To reproduce the issue, simply have two sites in IIS, configured with unique application pools, being ran as the user. After you go to one websites PHP Application, with 5.2.17, you will get a blank page. This also happens when you try to run 5.3.10, and 5.2.17 at the same time on a server. If you use the version below 5.2.13, you will not encounter this issue. I have been running it for a few months without having this problem. I hope this helps someone out, please +1 me if it does!
I put it under c:\php\ZendServer, you can put it wherever you want, make sure you update your *.ini files to point to the right place, I also included ioncube.
Download link: Zend Server 5.2.13+1 this post if it helped you!