Can't select "Normal to Surface" when Sweeping

Hello,

I am trying to make a Sweep feature (or a Swept Blend - both have the same problem) with multiple adjacent curves as references (I don't add them as separate Trajectories, instead going to Trajectories >> Details and inputting them as references). However, as soon as I add the second curve, I lose the option to select "Normal to Surface" for horizontal/vertical control. Does anyone know how this might happen?