i got this error in the rhino dialog box this eve. not sure what it means, or why it popped up, as i ran this definition a couple times before w/ no problems.
Hello Stu,
I quickly tested your definition and I think I understand what happens: there are null references on the canvas (the orange component). I think that the fact that GH cannot recover better is due to some changes in GH 0.6.19. If you either delete the orange "Geometry parameter" or assign it to something, the alert does not appear again. Hope it helps.
thanks for the report. This is indeed a bug. It's been caught in time to prevent a Rhino-wide crash, but it does mean that the viewport preview gets short-circuited.
I'll get it fixed for the next release. In the meantime, Giulio's solution should help you out.