Fatal error: Uncaught Error: Class "PKP\plugins\Plugin" not found in C:\xampp\htdocs\ojs\lib\pkp\classes\plugins\OAIMetadataFormatPlugin.php:19 Stack trace: #0 {main} thrown in C:\xampp\htdocs\ojs\lib\pkp\classes\plugins\OAIMetadataFormatPlugin.php on line 19