Upload archivos via FTP

[sataca]

Tengo el siguiente código:

$ftp_server="xxx.xxx.xx";
$ftp_user_name="aaaa";
$ftp_user_pass="bbb";
$conecta= ftp_connect($ftp_server);

// login with username and password
$login_result = ftp_login($conecta,$ftp_user_name, $ftp_user_pass);

// check connection
if ((!$conecta) || (!$login_result)) {
echo "FTP connection has failed!";
echo "Attempted to connect to $ftp_server for user $ftp_user_name";
exit;
} else {
echo "Connected to $ftp_server, for user $ftp_user_name";
}

$destination_file="img/$image_data_name";

//upload the file
$upload = ftp_put($conecta, $destination_file, $image_data_name, FTP_IMAGE);

// check upload status
if (!$upload) {
echo "FTP upload has failed!";
} else {
echo "Uploaded $source_file to $ftp_server as $destination_file";
}
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Esto viene de un formulario con un campo tipo file llamado image_data.

Me da el siguiente error al tratar de subir una imagen (Muestra.jpg):

"Warning: error opening Muestra.jpg in /home/html/bac/ftp.php on line 43"

Line 43 es esta:
$upload = ftp_put($conecta, $destination_file,

¿que coño está pasanado??

saludos y gracias