Hi gara, the sub-d plug-in requires the object's faces to be quads or triangles, meaning all faces should have 3 or 4 boundary edges on them.

If you have something like a 5-sided pentagonal face in your object for example, that object will not be usable by the plugin and you'll get an error and behavior like you describe.

My guess is that's what you're running into, if you're not sure then please post the 3DM model file of your object so I can take a look at your particular case.

You would need to edit the model to be made up of quad faces before you can subdivide it, you can do this by drawing in some lines and using Edit > Trim to cut things into quads, or you also might try exporting out from MoI as an .obj file using the "Output: Quads & Triangles" option (not n-gons) and then importing that back in again.

- Michael