Fatal error: Uncaught Error: Undefined constant "PKP\oai\PKP_STRICT_MODE" in C:\xampp\htdocs\ojs\lib\pkp\classes\oai\OAIRepository.php:51 Stack trace: #0 {main} thrown in C:\xampp\htdocs\ojs\lib\pkp\classes\oai\OAIRepository.php on line 51