[root@smash ~] packstack --answer-file /root/answers.txt
Welcome to Installer setup utility

Installing:
Clean Up                                             [ DONE ]
Setting up ssh keys                                  [ DONE ]
Discovering hosts details                        [ ERROR ]

ERROR : Failed to run remote script, stdout:
stderr: ssh_exchange_identification: Connection closed by remote host

Please check log file /var/tmp/packstack/20140806-095144-1xL4KI/openstack-setup.log for more information

Here is the tail of setup.log

File "/usr/lib/python2.6/site-packages/packstack/installer/setup_controller.py", line 68, in runAllSequences
    sequence.run(config=self.CONF, messages=self.MESSAGES)
  File "/usr/lib/python2.6/site-packages/packstack/installer/core/sequences.py", line 98, in run
    step.run(config=config, messages=messages)
  File "/usr/lib/python2.6/site-packages/packstack/installer/core/sequences.py", line 44, in run
    raise SequenceError(str(ex))
SequenceError: Failed to run remote script, stdout:
stderr: ssh_exchange_identification: Connection closed by remote host