PHPBB Email Error

This error keeps cropping up:

Failed sending email :: PHP ::


Line : 234
File : emailer.php

I contacted PHPBB support and they said to do a sendmail test. I did and it worked fine. This error just pops up at random and goes away on its own in a few minutes or hours. Does anyone know what might cause this? On line 234 is this:

message_die(GENERAL_ERROR, 'Failed sending email :: ’ .
(($this->use_smtp) ? ‘SMTP’ : ‘PHP’) . ’ :: ’ . $result, ‘’, LINE,

No changes were made to that page. No mods or hacks are installed.