Cant send e-mail by php mail on first attempt - forms

Question

I'm trying to send an email via SMTP using PHPMailer on my site, it works the second time I try (use submit), but the first time it says it cannot authenticate, login or password is invalid. I have searched a lot and can't find the answer, can someone help me please?
By the way I'm using JSON to get the PHP response in an alert. My host doesn't have "smtp." in front because support told me to do it this way.
This is the code:
else {
$phpmail = new PHPMailer();
$phpmail->IsSMTP(); // envia por SMTP
$phpmail->Host = "velvetwebdesign.com.br"; // SMTP servers
$phpmail->Port = "587"; // Port
$phpmail->SMTPAuth = true; // Caso o servidor SMTP precise de autenticação
$phpmail->SMTPDebug = 1;
$phpmail->Username = "email#velvetwebdesign.com.br"; // SMTP username
$phpmail->Password = "xxxxxxx"; // SMTP password
$phpmail->IsHTML(true);
$phpmail->From = 'email#velvetwebdesign.com.br';
$phpmail->FromName = $_POST['nome'];
$phpmail->AddAddress("velvetwebdesign#velvetwebdesign.com.br");
$phpmail->AddAddress($_POST['email']);
$phpmail->Subject = 'Contato Velvet Web Design';
$phpmail->Body .= "<b>Cliente:</b> ".$_POST['nome']."<br />";
$phpmail->Body .= "<b>E-mail:</b> ".$_POST['email']."<br />";
$phpmail->Body .= "<b>Telefone:</b> ".$_POST['telefone']."<br />";
$phpmail->Body .= "<b>Assunto:</b> ".$_POST['assunto']."<br /><br />";
$phpmail->Body .= "<b>Mensagem:</b><br />".nl2br($_POST['mensagem'])."<br /><br />";
$phpmail->Body .= "Recebemos a sua mensagem, responderemos em breve.<br />";
$phpmail->Body .= "http://www.velvetwebdesign.com.br/";
$send = $phpmail->Send();
if($send){
echo "A Mensagem foi enviada com sucesso. Enviaremos uma copia para o seu e-mail tambem.";
exit;
}else{
echo "Tente novamente por favor. Erro: " .$phpmail->ErrorInfo;
exit;
}
}
?>