Is it the brake cable housing or the inner wire that's giving you problems? Campy brake inner wires have a slightly different end fitting than Shimano et. al and, unless they are Campy specific or modified to fit, they may not seat properly.
BTW, Campy shift inner wires definitely have different diameter end fittings than Shimano and using the wrong wires can result in nearly hopeless jams when it come time to change them.