551 FTP Reply Code - KB Article #1534Related Articles --
551 Requested action aborted: page type unknown.
A 551 reply code may be sent in response to any command requiring the server to store information locally. It is a permanent negative reply, which means the client is discouraged from sending the command again since the server will respond with the same reply code. It is only applicable when the page file structure is being used (through a "STRU P" command).