file upload problem - Warning: ftp_put(): error opening ...

I'm writing an upload script to upload directly to a remote server. It seems to connect ok but I can't 'put' the file.
This is the error:
Warning: ftp_put(): error opening in /home/virtual/site279/fst/var/www/html/fileupload3/upload.php on line 24

Here is my code
<?php
$ftp_server="glasswing.com";
$conn_id = ftp_connect($ftp_server);
$user="XXX";
$passwd="FOO";
$login_result = ftp_login($conn_id, $user, $passwd);
if ((!$conn_id) || (!$login_result)) {
echo "FTP connection has failed!";
echo "Attempted to connect to $ftp_server for user $ftp_user_name";
die;
} else {
echo "Connected to $ftp_server, for user $user";
}
//directorylike /www.velibaba.com/images
//ftp_chdir($conn_id, "www.velibab.com");
//ftp_chdir($conn_id, "compimages");
//$destination_file=ftp_pwd($conn_id);
$destination_file="x.jpg";
echo ("");
print $destination_file;
echo ("");
// upload the file
$source_file = $_POST['userfile'];
$upload = ftp_put($conn_id, $destination_file, $source_file, FTP_BINARY);
// check upload status
if (!$upload) {
} else {
echo "Uploaded $source_file to $ftp_server as $destination_file";
}
// close the FTP stream
ftp_close($conn_id);
?>

Thanks!

Have you checked out this link?

http://www.php.net/manual/en/function.ftp-put.php

Try the suggestions on that page. Hopefully that will help you.