can't ssh to centos6.5 instance in fuel6.0+

After we deployed openstack by fuel6.0+(fuel6.0 & fuel6.1), we launched an instance with centos images downloaded from OpenStack org web. However, we can't ssh to that instances after we associated floating ip. But we can ssh to ubuntu instance.
we checked log and found that the sshd service start failed with the error information--"avc: denied".