Error with Failed Ajax request or invalid JSON returned

hello, i have this problem.

Failed Ajax request or invalid JSON returned.

my php log is:

PHP Fatal error: Uncaught Error: Failed opening required ‘./lib/pkp/includes/functions.inc.php’ (include_path=’.:/usr/share/php’) in /var/www/html/ojs-3.3.0-6/lib/pkp/includes/bootstrap.inc.php:36\nStack trace:\n#0 /var/www/html/index.php(65): require()\n#1 {main}\n thrown in /var/www/html/ojs-3.3.0-6/lib/pkp/includes/bootstrap.inc.php on line 36

PHP Fatal error: Declaration of ManageCopyeditFilesForm::execute($stageSubmissionFiles, $fileStage = null) must be compatible with ManageSubmissionFilesForm::execute($stageSubmissionFiles = null, $fileStage = null, …$functionArgs) in /var/www/html/restore/ojs-3.3.0-6/lib/pkp/controllers/grid/files/copyedit/form/ManageCopyeditFilesForm.inc.php on line 33

PHP Fatal error: Uncaught Error: Failed opening required ‘./lib/pkp/includes/functions.inc.php’ (include_path=’.:/usr/share/php’) in /var/www/html/ojs-3.3.0-6/lib/pkp/includes/bootstrap.inc.php:36\nStack trace:\n#0 /var/www/html/index.php(65): require()\n#1 {main}\n thrown in /var/www/html/ojs-3.3.0-6/lib/pkp/includes/bootstrap.inc.php on line 36

Application Version - e.g., OJS 3.3.0-6: