Fatal error: PHP warning in file /users/crazy-tools/www/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 /users/crazy-tools/www/Forum/wcf/lib/system/event/EventHandler.class.php (73): get_class() expects parameter 1 to be object, string given
error code: 0
file: /users/crazy-tools/www/Forum/wcf/lib/system/WCF.class.php (255)
php version: 5.3.2
wcf version: 1.0.10 (Horizon)
date: Thu, 08 Apr 2010 20:07:47 +0000
request: /Forum/acp/index.php?packageID=25
referer:

Stacktrace:
#0 [internal function]: WCF::handleError(2, 'get_class() exp...', '/users/crazy-to...', 73, Array)
#1 /users/crazy-tools/www/Forum/wcf/lib/system/event/EventHandler.class.php(73): get_class('UserAuth')
#2 /users/crazy-tools/www/Forum/wcf/lib/system/event/EventHandler.class.php(142): EventHandler::executeInheritedActions('UserAuth', 'loadInstance', 'UserAuth', 'loadInstance@Us...')
#3 /users/crazy-tools/www/Forum/wcf/lib/system/auth/UserAuth.class.php(28): EventHandler::fireAction('UserAuth', 'loadInstance')
#4 /users/crazy-tools/www/Forum/wcf/lib/system/session/SessionFactory.class.php(115): UserAuth::getInstance()
#5 /users/crazy-tools/www/Forum/wcf/lib/system/session/SessionFactory.class.php(71): SessionFactory->create()
#6 /users/crazy-tools/www/Forum/wcf/lib/system/WCFACP.class.php(58): SessionFactory->get()
#7 /users/crazy-tools/www/Forum/wcf/lib/system/WCFACP.class.php(30): WCFACP->initSession()
#8 /users/crazy-tools/www/Forum/acp/global.php(21): WCFACP->__construct()
#9 /users/crazy-tools/www/Forum/acp/index.php(7): require_once('/users/crazy-to...')
#10 {main}