This is decidedly odd. I found that the endpoints in the head and neck weren't exactly the same as the target figure (no idea why, now) - and neither were the orientation values. I corrected them both and it worked... I even had a corrected CR2 ready for download.

Then I thought I might do a quick render to show everyone how clever I was. Vicki got a hairball again, and it hasn't worked since.

Ok, back to the drawing board. :-(