What could be the cause of this?
You’re probably running Rhino with .NETCore, while this method that is missing is only in .NETFramework. Run the SetDotNetRuntime command in rhino, choose the framework, restart rhino and that shroud fix this, I think.
Heyy sorry I’m on Mac 
I’m sorry to tell you, but same problem except no solution I’m afraid. The developer should make their toolbox cross-platform.
Hi Menno,
Thank you for this solution it worked in my case. But I wonder what are the implications of changing the NET method from core to framework? might it cause other issues?
All the best,
Y