I'm trying to use the birail tool and it should be so simple, but I'm not getting good results. Maybe I'm using the wrong tool but I have a closed shape, with 2 paths that emminate from the shape. What I get is only half a sweep. How do I get the whole shape to sweep along those paths?

What I'm doing is selecting the source shape, activating >Surfaces > Birail > Birail 1 Tool. With the default settings (and many other experiments) I then select the 2 paths but the result is always the same... an incomplete sweep.

Very odd.