how do I do this in "sweep"?

 From:  Rudy
549.1 
Michael,
again me, Rudy.
I want to create a solid, half-rounded loop with "sweep" option (see attachment)
But I cannot make this
....
I select the sweep button. select the profiles ( first the two half-curves, then the two connecting lines), when prompted for the rail(s), select the circle,
and nothing happen.

why?

Thank you,
Rudy