Pipe not working for open curve

Rhino Rhino for Windows
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1

I’m running Version 7 SR10 (7.10.21256.17001, 2021-09-13).

I cannot get the Pipe command to do anything on a curved open curve. The below screenshot shows the selected rail (a simple curved open curve) and the start and end radii specified. I am about to press Enter, as there are no more radii:

2021-10-16
2021-10-161155×865 94.8 KB

After pressing Enter, I get this:

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2021-10-16 (1)1155×865 95 KB

No pipe is created and the Pipe command is not in the Undo history. If I do the exact same thing on a straight line segment (again, an open curve) it works. My objective is to get a curved pipe with constant radius whose axis is the selected open curve. Why can’t I get this to work?

The file containing the open curve is here:
Pipe Problem.3dm (25.9 KB)

2

Hi Mike- there are two stacked control points at the lower end of the curve.

-Pascal

3

Thanks. It would be nice if Rhino could provide suggestions, hints… something when commands fail.