If you still need to chain your geometry into a curve, click the Curve chaining button and chain the curve. See Overview of Chaining for more information.
Click the Pick curve 
button. The dialog box warps into a small button. Click the geometry or curve in the graphics window. The curve must be in the XY plane of the current setup. The Z value of the lower curve does not matter. It is later transformed to the plane of the upper curve and the translated back down by the Thickness.
When you have selected the curve click Next.
