I don't think unlink() and ftp_put() are playing nice...

order_to_warehouse.php

<?php

// ...

// send file to warehouse
$conn_id = ftp_connect($ftp_server);
$login_result = ftp_login($conn_id, $ftp_user_name, $ftp_user_pass);

if ((!$conn_id) || (!$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";
}

$upload = ftp_put($conn_id, $ftp_destination, $ftp_source, FTP_BINARY);

if (!$upload) {
//    echo "FTP upload has failed!";
} else {
//    echo "Uploaded $source_file to $ftp_server as $destination_file";
	unlink($ftp_source);
}

ftp_close($conn_id);