My error is:
Plug-in could not be activated because it triggered a fatal error.
Your information on the WordPress site for plug-ins says nothing about other items/applications being required to run this plug-in.
I didn't know what a ZEND OPTIMIZER is, but now I realize it's a server side application/service to shield your PHP code.
I believe it'd be nice of you to at least post that 'an ancillary product is required to use this plug-in'. It might save others time and save you the headache of fielding support issues.
For your reference, I'm using GoDaddy as host solution and apparently they don't have this service installed.
Until next time,