Why SceneTexture:WorldNormal has an error message?

So I was following the UE4 tutorial that they have on their website for cel-shading, but when I got to the part where we have to do the inside lines and need to switch SceneTexture to WorldNormals I always get an error. I have redone this three times and every time there is an error. Anyone know why?

I just figured it out. I didn’t see the explanation below saying it won’t work in forward rendering.