WCF::handleException() Unhandled exception: Call to undefined method wcf\data\category\Category::isDisabled()

#0 /var/www/vhosts/schueler-forum.com/httpdocs/wcf/lib/page/AbstractPage.class.php(276): wcf\page\PartnerPage->assignVariables()
#1 /var/www/vhosts/schueler-forum.com/httpdocs/wcf/lib/page/AbstractPage.class.php(100): wcf\page\AbstractPage->show()
#2 /var/www/vhosts/schueler-forum.com/httpdocs/wcf/lib/system/request/Request.class.php(58): wcf\page\AbstractPage->__run()
#3 /var/www/vhosts/schueler-forum.com/httpdocs/wcf/lib/system/request/RequestHandler.class.php(139): wcf\system\request\Request->execute()
#4 /var/www/vhosts/schueler-forum.com/httpdocs/index.php(10): wcf\system\request\RequestHandler->handle('wbb')
#5 {main}