WCF::handleException() Unhandled exception: Class 'wcf\system\user\storage\UserStorageHandler' not found

#0 [internal function]: wcf\data\user\User->getGroupIDs()
#1 /mnt/web304/d1/46/58624246/htdocs/forum/wcf/lib/data/DatabaseObjectDecorator.class.php(85): call_user_func_array(Array, Array)
#2 /mnt/web304/d1/46/58624246/htdocs/forum/wcf/lib/page/UserPage.class.php(176): wcf\data\DatabaseObjectDecorator->__call('getGroupIDs', Array)
#3 /mnt/web304/d1/46/58624246/htdocs/forum/wcf/lib/page/AbstractPage.class.php(276): wcf\page\UserPage->assignVariables()
#4 /mnt/web304/d1/46/58624246/htdocs/forum/wcf/lib/page/UserPage.class.php(207): wcf\page\AbstractPage->show()
#5 /mnt/web304/d1/46/58624246/htdocs/forum/wcf/lib/page/AbstractPage.class.php(100): wcf\page\UserPage->show()
#6 /mnt/web304/d1/46/58624246/htdocs/forum/wcf/lib/system/request/Request.class.php(58): wcf\page\AbstractPage->__run()
#7 /mnt/web304/d1/46/58624246/htdocs/forum/wcf/lib/system/request/RequestHandler.class.php(139): wcf\system\request\Request->execute()
#8 /mnt/web304/d1/46/58624246/htdocs/forum/index.php(10): wcf\system\request\RequestHandler->handle('wbb')
#9 {main}