line 150 is an echo:
echo "<strong>".$row_rs_venue_loop['CUSTID']."</strong> : <span style=\"color: #F00;\">". $row_rs_venue_loop['Pub']."</span>, ".$row_rs_venue_loop['Address1'].", ".$row_rs_venue_loop['PostCode']."<br />";
causing html output to the page, which cases the error.
change it to:
$MailBody = $MailBody . "<strong>".$row_rs_venue_loop['CUSTID']."</strong> : <span style=\"color: #F00;\">". $row_rs_venue_loop['Pub']."</span>, ".$row_rs_venue_loop['Address1'].", ".$row_rs_venue_loop['PostCode']."<br />";
so it will be concatenated to the mail body string instead of echoing it.