Extend curve fails on this curveThroughPoints created curve at one end

Hi,
points planar (projected to surface and input deleted, after they were distorted with cage Edit)

selected the grouped set of points
use curve through points, curve type interpolated, degree 3 knots uniform

then hit enter etc.

noticed curve went a tad beyond last point.

then curve extendCurve and fails on the southern end.
extend curve fails.3dm (2.4 MB)

Steve

One of your points is duplicated. Ungroup the points and create the curve using only one point at each location.