I can select the body bone of the multiball rig but it seems the spin bone is gone. I can see 'spin' when I look at the bone group but when I select it it's non existent. Is there a way to rectify this?
It may be hidden, or the bone layer is not visible.
Try alt+h.
Also make sure you have run the script in the text editor. This will give you the buttons to control turning on/off these layers.
thanks!