wall joint

[nferroURLQ8]

Why I just can't make this corner joint correctly? these walls have the same height and are the same type, when I go to the geometry options, it does not allow me to miter it. Please help. 

[SteveKStafford]

Please share a 3D view of that corner. What is that to the left of the corner, a railing?

[nferroURLQ8]

It occurred me to shorten the fence, as you said, which is actually a rail. And I did unlock both walls' centerlines and magically worked! Now all the geometries options are also unlocked 🙂

What exactly is the one to blame?