Thank you. Since, I compared database tables of my OJS2.4.8.5 with a fresh installation and deleted unnecessary tables which were mixed during a failed upgrade. Now, I changed lib/pkp/classes/security/UserGroupDAO.inc.php line 88 from…
return $this->getInsertId();
…to…
return $userGroup->getId();
and tried upgrading from OJS 2.4.8.5 to OJS 3.0.0. Thank you so much, Successfully upgraded to version 3.0.0.0 I am so happy as the database cleanup took years. I will further try to upgrade to the latest versions step by step.