Need to re-identify keyboard...

Folloing solved it for me:

sudo rm /Library/Preferences/com.apple.keyboardtype.plist

and then reboot. After reboot the Assistant aks again, bingo !

Have you tried searching Help for changing keyboard type?
{quote}When you connect a keyboard that is not immediately recognized, Keyboard Setup Assistant automatically opens so that you can specify the keyboard type (ANSI, JIS, or ISO). There are three keyboard types that Mac OS X recognizes: ISO (Europe), JIS (Japan), and ANSI. The ANSI keyboard is a standard 101-key layout widely used in the U.S., North America, and many other parts of the world.

If you’re having trouble with your keyboard, you may need to specify the type manually. You can use Keyboard & Mouse preferences to open Keyboard Setup Assistant and specify the keyboard type.

To specify the keyboard type:

Choose Apple menu > System Preferences, and then click Keyboard & Mouse.

Click Keyboard.

Click the Change Keyboard Type button.

Follow the onscreen instructions when Keyboard Setup Assistant appears.
{quote}

Contact the keyboard manufacturer.

Same problem here! No "Change Keyboard Type" button and the KeyboardSetupAssistant isn't starting. ("No unknown keyboard connected - terminating")

Very frustrating.