Is Planar Definition Error: Data conversion failed from Curve to Surface

Hello! I am working on a great tutorial by Rhino Grasshopper on YouTube.
https://youtu.be/ODeL9POG_FM.

By the 7:14 mark I have an issue with the “Is Planar” definition. It gives me this message: “1. Data conversion failed from Curve to Surface”

Attached is the gh file so far up to minute 7:14. Please note that I work on Rhino 5 with Grasshopper WIP (0.9.0076) I’m not sure if that may be a factor or not.

073 Diamond Pattern Box _ver 2 Rhino Grasshopper Tutorial.gh (27.4 KB)

I appreciate your kind advice! Sincerely,

Gustavo