Hi eric - it's probably either that the file contains block instances or mesh objects.

To see which it is, select one of the objects in Rhino and then run the "What" command to see what kind of object it is.

If it's a block instance then use the Explode command in Rhino to break it down into regular geometry - MoI doesn't yet handle block instance objects from Rhino, they just get skipped.

Also if it's a polygon mesh type object in Rhino instead of a NURBS object those kinds of objects are also skipped when reading into MoI.

- Michael