The "lines" being seam edges of individual surfaces...??? THis is caused by having "corner points" in your rails. You can see these if you run seperate on your rail and it breaks into segments that match the surfaces created from the sweep.... You can get rid os them in a couple ways, like turning on control points and deleteing the points at these areas (While it is a joined curve). You can also run rebuild on the rails to get rid of them...