We found the problem.
Please add the code
function execute($task){
		if(substr($task,0,12)=='triggerplug-'){
			JPluginHelper::importPlugin( 'hikashop' );
			$dispatcher =& JDispatcher::getInstance();
			$parts = explode('-',$task,2);
			$event = 'onTriggerPlug'.array_pop($parts);
			$dispatcher->trigger( $event, array( ) );
			return true;
		}
		return parent::execute($task);
	}before the line:
function display($cachable = false, $urlparams = false){
in the file administrator/components/com_hikashop/helpers/helper.php and that should then work.