Hi Rudy, it looks like your sweep result is not closed, if you zoom in to this area a bit you can see a gap:





It looks like this is because your rail curve is made up of 2 segments that are not smooth in the area that they touch each other there, one way to smooth that out would be to select the control point where the 2 segments touch and delete it.

How did you create that rail curve? It looks like it might be the result of some projection or intersections between other pieces? Do you have the original pieces that were used to project or intersect with? Those original pieces may have a crease in between them as well.

- Michael