536 FTP Reply Code - KB Article #1541Related Articles --
536 Requested PROT level not supported by mechanism.
A 536 reply code may be sent in response to a PROT command when the requested protection level is unsupported by the current security mechanism. 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. Negotiating a different security mechanism using the AUTH command may result in a different reply code.