Same error here on gnome 32 but only when attacking locally
If I attack my external ip the attack works fine...
ncrack -vv --user root 192.168.0.9:22
Starting Ncrack 0.3ALPHA ( http://ncrack.org ) at 2011-05-26 07:32 PDT
Invalid service module: ssh
Notice it doesn't crack anything but that's only because the service isn't forwarded to begin with.
ncrack -vv --user root 188.8.131.52:22
Starting Ncrack 0.3ALPHA ( http://ncrack.org ) at 2011-05-26 07:38 PDT
Ncrack done: 1 service scanned in 3.00 seconds.
Probes sent: 1 | timed-out: 1 | prematurely-closed: 0