Well line 234 is
message_die(GENERAL_ERROR, 'Failed sending email :: ' . (($this->use_smtp) ? 'SMTP' : 'PHP') . ' :: ' . $result, '', __LINE__, __FILE__);
So from what it looks like is that your board settings when it comes to the email or your webhost, doesn't have something setup properly.
NOW for the forums I run I do not touch the email setup in the configuration. Meaning at the bottom of the configuration page in the admin panel where it says "Use SMTP Server for email" I have it at NO and the rest of the fields below it are left empty. And the people still get the emails and pm'* and stuff.
Maybe have a look there and see what you have setup.