We may reach a situation where we cannot access the plesk control panel and the web mail after installing the Zend Optimizer.
During the installation process, Zend sets a value for php.ini file in the registry.
HKEY_LOCAL_MACHINE\SOFTWARE\PHP\IniFilePath=C:\WINDOWS
Therefore, all .php scripts on the server start to use this setting and go to C:\WINDOWS\php.ini file for PHP configuration.
To fix this problem it’s necessary to clear the value
HKEY_LOCAL_MACHINE\SOFTWARE\PHP\IniFilePath.
Then all .php scripts will start to use correct .ini files.