550 error means that the ftp user does not have sufficient privileges to perform the action on which this error occurred.
In your case, it fails while trying to create the bin folder. It might fail if the bin folder already exists?
Or does the user has enough privileges to create that folder in the given path level. Maybe you are trying to create it on the root place of your hosting but don't know if you have access to create folders with this user in the root.
Please check this for more info :
550
550