Can solve my "SMTP Error: Could not authenticate" error - php

Question

i have a problem with my PHPmailer function.
I want my registration form to send a mail to every new registered member.
I get this error code. SMTP Error: Could not authenticate.
I have contacted my webhost, and they say that i have the right username,password, smtp server etc.
include "class.smtp.php";
include "class.phpmailer.php";
$Host = "mail.smtp.com"; // SMTP servers
$Username = "support#mymail.com"; // SMTP password
$Password = "mymailpassword";
$From = "support#mymail.com";
$FromName = "My name";
$ToEmail = $mail;
$ToName = $username;
$header = str_replace('%homepage_url%', $hp_url, $_language->module['mail_subject']);
$Message = str_replace(Array('%nickname%', '%username%', '%password%', '%activationlink%', '%pagetitle%', '%homepage_url%'), Array(stripslashes($nickname), stripslashes($username), stripslashes($pwd1), stripslashes($validatelink), $hp_title, $hp_url), $_language->module['mail_text']);
$mail = new PHPMailer();
$mail->IsSMTP(); // send via SMTP
$mail->Host = $Host;
$mail->SMTPAuth = true; // turn on SMTP authentication
$mail->Username = $Username;
$mail->Password = $Password;
$mail->From = $From;
$mail->FromName = $FromName;
$mail->AddAddress($ToEmail , $ToName);
$mail->WordWrap = 50; // set word wrap
$mail->Priority = 1;
$mail->IsHTML(true);
$mail->Subject = $header;
$mail->AltBody = "To view the message, please use an HTML compatible email viewer!"; // optional, comment out and test
$mail->MsgHTML($Message);
$mail->CharSet="UTF-8";
if(!$mail->Send()){
redirect("index.php",$_language->module['register_successful'],10);
$show = false;
} else {
redirect("index.php",$_language->module['register_successful'],10);
$show = false;
}