PHPMailer出错Couldnotinstantiatemailfunction

PHPMailer 报错 Could not instantiate mail function.
我在phpmailer官网下载的最新的库，根据里面自带的test下的测试文件配置的，php.ini里面也支持sockets。上网查了许多资料也都试了还是不行，故在此请教各位大神指点指点，不胜感激！！！

/**
* Simple example script using PHPMailer with exceptions enabled
* @package phpmailer
* @version $Id$
*/

require '../class.phpmailer.php';

try {
	$mail = new PHPMailer(true); //New instance, with exceptions enabled

	$body             = file_get_contents('contents.html');
	$body             = preg_replace('/\\\\/','', $body); //Strip backslashes

	$mail->IsSMTP();                           // tell the class to use SMTP
	$mail->SMTPAuth   = true;                  // enable SMTP authentication
	$mail->Port       = 25;                    // set the SMTP server port
	$mail->Host       = "smtp.163.com"; // SMTP server
	$mail->Username   = "[email protected]";     // SMTP server username
	$mail->Password   = "***";            // SMTP server password

	//$mail->IsSendmail();  // tell the class to use Sendmail

	$mail->AddReplyTo("[email protected]","First Last");

	$mail->From       = "[email protected]";
	$mail->FromName   = "phpmailer";

	$to = "[email protected]";

	$mail->AddAddress($to);

	$mail->Subject  = "First PHPMailer Message";

	$mail->AltBody    = "To view the message, please use an HTML compatible email viewer!"; // optional, comment out and test
	$mail->WordWrap   = 80; // set word wrap

	$mail->MsgHTML($body);

	$mail->IsHTML(true); // send as HTML

	$mail->Send();
	echo 'Message has been sent.';
} catch (phpmailerException $e) {
	echo $e->errorMessage();
}
?>

------解决方案--------------------
给出你的下载地址

可能是要求的 php 版本太高了吧？
------解决方案--------------------
//$mail->IsSendmail();
这个去掉的话默认是使用系统的mail函数发送邮件的。会不会是这个原因。