PHP extension "Zend Optimizer|Zend Guard Loader" is not loaded.

Hi to all

I  encountered  this error during CMS Server tester


Error:
CMS Server Tester
Your server was tested to meet all CMS requirements. Following errors were encountered an need to be fixed to run the software:

    PHP extension "Zend Optimizer|Zend Guard Loader" is not loaded.
    Please verify your server configuration. Make sure that extension "Zend Optimizer|Zend Guard Loader" is enabled. [ Check for a possible solution here. ]

thank you for anyone who can answer to solved this