Have you checked if mod_imap is enabled? I got a white screen because of that during the setup.
To hack / debug and see if the problem goes away you can add:
if (class_exists('POP3')) die();
Add it right after the three includes in class.pop3.php so it looks like:
require_once(INCLUDE_DIR.'class.mailparse.php');
require_once(INCLUDE_DIR.'class.ticket.php');
require_once(INCLUDE_DIR.'class.dept.php');
if (class_exists('POP3')) die();
Report back with your findings.