array_key_exists(): Using array_key_exists() on objects is deprecated. Use isset() or property_exists() instead 
in '/disk0/disk1/data/piwik/libs/Zend/Registry.php' at the line 206

#0  Piwik_ErrorHandler(...) called at [/disk0/disk1/data/piwik/libs/Zend/Registry.php:206]
#1  Zend_Registry->offsetExists(...) called at [/disk0/disk1/data/piwik/libs/Zend/Registry.php:145]
#2  Zend_Registry::get(...) called at [/disk0/disk1/data/piwik/core/Session.php:30]
#3  Piwik_Session::isFileBasedSessions(...) called at [/disk0/disk1/data/piwik/core/FrontController.php:231]
#4  Piwik_FrontController->init(...) called at [/disk0/disk1/data/piwik/index.php:52]