GOLDEN NOTE: Pay close attention to the blue areas in the dialogue boxes. Though this should be paid attention to in ALL workbenches, the wireframe (and surfacing) workbench will be especially unforgiving if you select objects without heeding the selection boxes.

Also, remember that even though curves APPEAR to exist on surfaces, CATIA may not actually assume this to be true. It may sometimes be necessary to project a curve on to a surface, however connected they seem, in order to utilize the curve and surface together.