Grevit

Grevit allows you to create Revit or AutoCad Architecture BIM elements
directly in Grasshopper and send them to your favorite BIM program.

Grevit 'Revit extrusion' not exporting

Hi

I'm trying to export a simple Revit extrusion using Grevit. When Grevit connects to Revit, I am choosing a conceptual mass family template (or is generic model better?). However, I then get an error message: 

Revit could not complete the external command. Contact the provider for assistance. Information they provided to Revit about their identity: MTT.

What would be causing this? The mass is a simple polygon extrusion. Is it something to do with admin privileges?

Thanks