With "special:ask" I'm getting on mw 1.21 and smw 184.108.40.206:
Fatal error: Class 'SMW\ApiResultPrinter' not found in /mediawiki-1.21.1/extensions/SemanticResultFormats/formats/calendar/EventCalendar.php on line 42. After dropping that format I receive
Fatal error: Class 'SMW\ResultPrinter' not found in /mediawiki-1.21.1/extensions/SemanticResultFormats/formats/gallery/Gallery.php on line 38. I received similar complaints about Media Player, Tag Cloud, and Datatables. After dropping these, special:Ask displayed properly.
I've also tried jqplots and listwidget and they are unhealthy also.