To allow root login via ssh on FreeBSD, edit sshd_config file:
sudo vi /etc/ssh/sshd_config
Find this line:
#PermitRootLogin no
and change it to:
PermitRootLogin yes
Now Restart sshd:
root@Freebsd10:~ # /etc/rc.d/sshd restart
Performing sanity check on sshd configuration.
Stopping sshd.
Waiting for PIDS: 1698.
Performing sanity check on sshd configuration.
Starting sshd.