how to use vB_DataManager_Post_Multiple ?

[netwind]

I't trying delete multiply posts :

PHP Code:

 
 $postdm=& datamanager_init('Post', $vbulletin, ERRTYPE_ARRAY, 'threadpost');
 $postdm->set_condition("threadid=200 and not parentid = 0"); 
 $count_post+=$postdm->delete();
 $postdm->has_errors(true);
 unset($postdm); 


but nothing happens.
Is this class really functioning ?