jos-Error: Using $this when not in object context

plgSystemKoowa -> exceptionHandler()
JError :: raiseError() @ /srv/www/2/2/2/2224/www/www.eutonia.at/htdocs/plugins/system/koowa/koowa.php:233
JError :: raise() @ /srv/www/2/2/2/2224/www/www.eutonia.at/htdocs/libraries/joomla/error/error.php:251