php - 500 Internal Server Error - PHPMailer -

i'm trying include class.phpmailer.php file reason whenever add require_once code, whole page breaks , gives me 500 internal server error. func.php script located in coupons/inc/ on ftp server , class.phpmailer.php file in same place.

ini_set("include_path", '/home/busaweb/php:' . ini_get("include_path") ); include('mail.php'); include('mail/mime.php'); require_once(root_path . "/coupon/inc/class.phpmailer.php"); 

is there wrong .htaccess or not using correct file path? thank you.

if include file in same directory use following:

require_once(dirname(__file__)."/class.phpmailer.php");