I can't really think of anything to write here now...
$forum = new stdclass()), but it is attempting to call a method for stdclass::update which will never exist (stdclass has no method update and PHP doesn't allow a way to trait into a stdclass object [at least I don't think it does]). So the issue is simply that $forum is not of the correct datatype. Why it isn't is unknown; for that you need to determine the creation sequence for the $forum variable and have it created as the correct type (maybe of a new Forum datatype?).
As for the above couple posts, love the randomness. I don't use any boxed CMS, but even I know that Joomla and Yii are different beasts.