Please help me with this code

[Fidox]

In my php application I got this function

require_once('./global.htm');
require_once('./includes/class_dm.htm');
require_once('./includes/class_dm_threadpost.htm');

function update_thread($title, $pagetext, $threadid) {
  global $vbulletin;
  $postdm =& datamanager_init('Post', $vbulletin, ERRTYPE_ARRAY, 'threadpost');
  $threadinfo = fetch_threadinfo($threadid); 
  $foruminfo = fetch_foruminfo($threadinfo['forumid']); 
  $postinfo = fetch_postinfo($threadinfo['firstpostid']);
  $userinfo = fetch_userinfo($postinfo['userid']);
  $postdm->set_info('forum', $foruminfo); 
  $postdm->set_info('thread', $threadinfo);
  $postdm->set_info('post', $postinfo);
  $postdm->set_info('user', $userinfo);
  $postdm->set('title', $title); 
  $postdm->set('pagetext', $pagetext);
  $postdm->pre_save(); 
  if (count($postdm->errors) > 0) { 
    print_r($postdm->errors);
    return FALSE;
  } else { 
    print_r($postdm->errors);
    echo $postdm->save();
    return TRUE;
  }
}

Function update_thread should find thread by its id and update title and pagetext of its first post. The problem is that at the end I am getting error "You did not specify a username for your post.". I would highly appreciate if you could help me to solve it or at least point me to the direction where I can find more samples how to use datamanager (it looks to be almost undocumented). Thank you.