Error now contains num of unaddable shape, in its shp file

Adding polylines to Rhino and Grasshopper with very closely spaced points, close to the floating point precision, can cause rs.AddPolyLine to raise an 'unable to add polyline to document' error. These closely spaced points are common in GIS co-ordinate systems and shapefiles from public sources.

There is little documentation available to say what the limits are in Rhino, and from experimenting simply with code snippets such as:
rs.AddPolyline([[840103.7448000005, 826915.3969999999], [840102.0987999998, 826918.7357999999], [840100.6714000003, 826921.5581], [840099.2468999997, 826924.4590000007], [840095.2278000005, 826925.2062999997], [840095.2275999999, 826925.2062999997]])

Rhino can be happy with a 2-point, close points polyline, but than an extra point in that polyline can cause this error too.