I'm pretty sure Dave nailed it, when you round inner edges it always skins the hole and it just needs to be deleted. [image: HwTF_Skin.gif]

Yes! small objects that are processed by native tools [e.g. FollwMe] OR plugins making meshes etc can fail to make tiny facets, if they would have edges <1/1000" long. SketchUp's in-built tolerance assumes the two point specified for such tiny edge's ends are coincident. Therefore the tiny edge is not make and the face that needed it fails to be created too. If you Scale your original object up by say 100, then the smaller facets will still be big enough to get made. Afterwards you just Scale back down to the desired size. The tiny facets will survive that Scaling down - tiny geometry can exist - but SketchUp can't create it initially.