Fatal error: PHP warning in file /mnt/web1/a0/93/51768093/htdocs/forum/wcf/lib/system/event/EventHandler.class.php (73): get_class() expects parameter 1 to be object, string given

Information:

error message: PHP warning in file /mnt/web1/a0/93/51768093/htdocs/forum/wcf/lib/system/event/EventHandler.class.php (73): get_class() expects parameter 1 to be object, string given
error code: 0
file: /mnt/web1/a0/93/51768093/htdocs/forum/wcf/lib/system/WCF.class.php (251)
php version: 5.3.29
wcf version: 1.0.6
date: Thu, 08 Dec 2016 19:58:45 +0000
request: /
referer:

Stacktrace:

#0 [internal function]: WCF::handleError(2, 'get_class() exp...', '/mnt/web1/a0/93...', 73, Array)
#1 /mnt/web1/a0/93/51768093/htdocs/forum/wcf/lib/system/event/EventHandler.class.php(73): get_class('UserAuth')
#2 /mnt/web1/a0/93/51768093/htdocs/forum/wcf/lib/system/event/EventHandler.class.php(142): EventHandler::executeInheritedActions('UserAuth', 'loadInstance', 'UserAuth', 'loadInstance@Us...')
#3 /mnt/web1/a0/93/51768093/htdocs/forum/wcf/lib/system/auth/UserAuth.class.php(28): EventHandler::fireAction('UserAuth', 'loadInstance')
#4 /mnt/web1/a0/93/51768093/htdocs/forum/wcf/lib/system/session/CookieSessionFactory.class.php(34): UserAuth::getInstance()
#5 /mnt/web1/a0/93/51768093/htdocs/forum/wcf/lib/system/session/SessionFactory.class.php(71): CookieSessionFactory->create()
#6 /mnt/web1/a0/93/51768093/htdocs/forum/lib/system/WBBCore.class.php(201): SessionFactory->get()
#7 /mnt/web1/a0/93/51768093/htdocs/forum/wcf/lib/system/WCF.class.php(91): WBBCore->initSession()
#8 /mnt/web1/a0/93/51768093/htdocs/forum/global.php(18): WCF->__construct()
#9 /mnt/web1/a0/93/51768093/htdocs/forum/index.php(7): require_once('/mnt/web1/a0/93...')
#10 {main}