Zend Optimizer Not Installed...but it IS installed
I've seen a lot of people struggling in the forums with the "Zend Optimizer Not Installed" error message for what seems to be a variety of reasons. Since I too received this message after having the calendar running fine for a couple of months after it's initial install, then "suddenly" we started receiving the Zend message, I thought I would post my follow-up in case anyone else has the same problem.
Our calendar is installed on a shared web host using an IIS web server.
After digging through the Easy PHP Calendar forums and spending time with the web host's tech support and getting no where, I went back to the web host and had them escalate my support ticket to their "server team."
The server team quickly responded and told me that the latest version of Zend Optimizer IS installed, but since I have my own PHP.INI file in my root web folder, Zend Optimizer is not detected and therefore will not run. I must delete my PHP.ini file in my web root so the web host's server level default PHP.ini file will be used instead.
This may seem like an easy solution, but we actually have a very important need for having our own PHP.ini file in our web root, so our dilemma continues.