I couldnt get it to work. I think I have version r14 now (for school, soon getting r15) but when I follow through the first steps, I dont get a wall. And when I lift any of them up (like, moving up) nothing happens, except for with the sweep nerbs, then the whole thing goes up xP
And I tried copying the rectangle, as well as the spline, in any way, but neither of them would work. With coping the spline and moving that up I came the closest, but for some reason the walls would thicken the higher I'd lift the spline >.<
Hey, sorry for taking so long to respond, I've been busy in non-DA related things lately.
Most probably your problem is corrected if you invert the order of the splines inside the sweep (1st spline should be second and viceversa). If that doesn't work, your rectangle is pointing in the wrong direction.