3.5p1, krb5 ssh -X-> sshd (F-Secure 3.0.1)?

[Phil]

I built openssh 3.5p1 with (--with-kerberos5=DIR) krb5-1.2.6 and
openssl 0.9.6g on RedHat 7.2 and been trying to get it to talk with a
commercial ssh, identified in the ssh -v output snippet below:

 .
 .
 .
debug1: Remote protocol version 1.99, remote software version 3.0.1 F-SECURE SSH SNL1.0
debug1: match: 3.0.1 F-SECURE SSH SNL1.0 pat 3.0.*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_3.5p1
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
 .
 .
 .
but it fails near the end like this:

 . 
 .
 .
debug1: newkeys: mode 1
debug1: SSH2_MSG_NEWKEYS sent
debug1: waiting for SSH2_MSG_NEWKEYS
debug1: newkeys: mode 0
debug1: SSH2_MSG_NEWKEYS received
debug1: done: ssh_kex2.
debug1: send SSH2_MSG_SERVICE_REQUEST
debug1: service_accept: ssh-userauth
debug1: got SSH2_MSG_SERVICE_ACCEPT
debug1: authentications that can continue: kerberos-tgt-2 at ssh.com,kerberos-1 at ssh.com,password,hostbased
debug1: no more auth methods to try
Permission denied (kerberos-tgt-2 at ssh.com,kerberos-1 at ssh.com,password,hostbased).
debug1: Calling cleanup 0x80641a4(0x0)


I've put 

 KerberosAuthentication yes

into ssh_config.

I'm not an expert, so any advice about what I'm missing would be
greatly appreciated.

TIA.