Error message

• Warning: Trying to access array offset on null in calendar_plugin_row->render() (line 439 of sites/all/modules/calendar/includes/calendar_plugin_row.inc).
• Warning: Trying to access array offset on null in calendar_plugin_row->render() (line 439 of sites/all/modules/calendar/includes/calendar_plugin_row.inc).
• Warning: Trying to access array offset on null in calendar_plugin_row->render() (line 439 of sites/all/modules/calendar/includes/calendar_plugin_row.inc).