Hi Klaus, in your attached file there seemed to be 3 long curves running in the rail direction so it wasn't entirely clear to me which of those 2 you had been trying to use as rails.

Like Steve mentions above though, usually for a sweep with rails coming to a shared point you don't want to have any tiny additional profile, just sweep the base profile by itself and that should do the job.

One additional thing though is your base profile is currently one long curved piece and then one little connecting line piece at the trailing edge - to get a solid the easiest thing would be to select those 2 profile pieces and use Edit > Join to join them together into a single connected profile curve, then sweep that. That will then form a solid directly after the sweep.

If you only sweep an open curve then you won't get a solid immediately, you would have to also construct something to fill in the gap where the little line segment is at.

I've attached a result with that base profile joined and using the 2 curves that touched each other at their tips as the rails, that has generated a solid.

- Michael