What is your PHP version ? It seems you use an obsolete version, Prestashop 1.7.4 can be used with PHP 5.6 minimum and PHP 7.1 maximum.
See https://devdocs.prestashop.com/1.7/basics/installation/system-requirements/
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What is our PHP version ? It seems you use an obsolete version, Prestashop 1.7.4 can be used with PHP 5.6 minimum and PHP 7.1 maximum.
See https://devdocs.prestashop.com/1.7/basics/installation/system-requirements/