>From your debug output it looks like the acquire credentials call is failing. This is somewhat strange. Have you created a host/<hostname> principal and correctly stored it in the machines keytab? Is this keytab readable by the sshd? Does the key version in the keytab match the one in the KDC?
If you have access to the logs of your KDC, you may find that it contains some more helpful information. Cheers, Simon.
