Hi Colin, the problem is that is a kind of unusual surface - your friend did not build it as a smooth surface, instead it is a single large degree 1 surface which means that even though it is a single surface it has a lot of sharp internal creases in it. Degree = 1 means that there is a straight line between each control point of the surface rather than there being a smooth curve between control points which is the more typical Degree = 3 case.

In normal usage, only a simple plane surface will have degree = 1.

MoI will take surfaces with internal creases like that and split them up, and the problem in this case appears to be in that splitting process, something involving the trimming boundaries is not getting split up properly, resulting in some pieces with an invalid trimming boundary. Invalid trimming boundaries can cause these kinds of meshing artifacts.

If he can get it to be split up in Rhino first and then export that to MoI it will probably solve the problem. One way to do that would be in Rhino run the ConvertToBeziers command on this surface, and then select all the little fragments and run Join on those to form a joined polysurface object rather than a "single surface with internal creases" type object.

Once you have it as a polysurface then bringing that into MoI will likely not have any issues.

The initial meshing problem in Rhino could also be related to this particular unusual surface construction of having a degree 1 surface with many points in it, making a creased surface.

Hope this helps,

- Michael