PHP FTP：访问被拒绝

<?php
error_reporting(E_ALL);
ini_set('display_errors',true);
flush();

$ftp_server = "myserver";
$ftp_user_name="myuser";
$ftp_user_pass="mypass";
$remote_file="myfile.txt";
$file="myfile.txt";

// set up a connection or die
$conn_id = ftp_connect($ftp_server) or die("Couldn't connect to $ftp_server"); 
$login_result = ftp_login($conn_id,$ftp_user_name,$ftp_user_pass);


if (ftp_put($conn_id,$remote_file,$file,FTP_ASCII)) {
 echo "successfully uploaded $filen";
} else {
 echo "There was a problem while uploading $filen";
}

// close the connection
ftp_close($conn_id);
 ?>

它在浏览器中给我一个警告

Warning: ftp_put(): Access is denied. in /var/www/html/ftpcheck.php on line 17. There was a problem while uploading myfile.txt.

我检查了文件的访问权限.但它可以访问.任何人都可以告诉我为什么会这样吗？