The regular sshd daemon and the gsi enabled gsisshd daemon can not both listen for connections on the same port. You can either deactivate the regular sshd before starting gsisshd or change the configuration of gsisshd to use a different port than the standard ssh port number 22. Common choices for an alternative port number are 23, 222 or 2222. If you configure gsisshd to only accept gsi connections and not accept other types of connections that require the existence of the ssh host keys, you can turn off the generation of these keys in /etc/sysconfig/gsisshd.