Re: Zend optimizer
You would need to find a newer version of the plugin script, or a version that isn't using Zend Guard/Zend Optimizer. Zend decided not to make their latest version compatible with older versions (they are aware of the problem, and have stated that they have no plans to fix it). Unfortunately, that means that scripts encoded for version 5.2 and earlier will not run on version 5.3 and later.
“Beware of bugs in the above code; I have only proved it correct, not tried it.” --Donald Knuth
"It was as if its architects were given a perfectly good hammer and gleefully replied, 'neat! With this hammer, we can build a tool that can pound in nails.'" -- Alex Papadimoulis (on TheDailyWTF.com)