ssh login fails: receive packet: type 51

http://www.snailbook.com/docs/assigned-numbers.txt
4.1.2.  Initial Assignments
         Message ID                            Value    Reference
         -----------                           -----    ---------
         SSH_MSG_USERAUTH_REQUEST                50     [SSH-USERAUTH]
         SSH_MSG_USERAUTH_FAILURE                51     [SSH-USERAUTH]



http://www.snailbook.com/docs/userauth.txt
6.  Authentication Protocol Message Numbers
   These are the general authentication message codes:

      SSH_MSG_USERAUTH_REQUEST            50
      SSH_MSG_USERAUTH_FAILURE            51
      SSH_MSG_USERAUTH_SUCCESS            52
      SSH_MSG_USERAUTH_BANNER             53

7.  Public Key Authentication Method: "publickey"

   The following method-specific message numbers are used by the
   "publickey" authentication method.

      SSH_MSG_USERAUTH_PK_OK              60