We run a lot of secure FTP with FTPS, typically using FileZilla Server on Windows servers.

If you find yourself seeing 550 errors while trying to upload files to the server, chances are your FileZilla server is running under the Windows SYSTEM account, and it does not have write access to the directory you are writing to. Save yourself some trouble by running FileZilla as a domain user (or local user) that you can ensure has permissions to the folder to where you are writing.