Hi Beetle, yes like Stefan mentions above, that 3DM file only contains polygon mesh objects in it, not any NURBS objects.

Rhino can write a lot of various kinds of different data to 3DM files, stuff like NURBS objects, spotlights, annotation text, dimensions, polygon mesh objects, etc... Of all those various kinds of data, MoI itself is only focused on working on NURBS data.

Polygon mesh data is structured differently than NURBS data, it's made up of a lot of little individual facets rather than large smooth surfaces. You will need to use a polygon mesh editing program to work with that kind of data, not MoI.

- Michael