you left a blank line between php tags at line 423. lines 421 - 424 are:
<?php require_once("webassist/email/mail_php.php"); ?>
<?php require_once("webassist/email/mailformatting_php.php"); ?>
<?php
change that to:
<?php require_once("webassist/email/mail_php.php"); ?>
<?php require_once("webassist/email/mailformatting_php.php"); ?>
<?php