1. Build two rail curves on the X and Z axis.
2. Build three or more rider curves and the Y and Z axis.
3. Hit the Birail 3+ tool (Surfaces > Birail > Birail 3+ Tool).
4. Select all the rider curves first. After you’ve select all the rider curves, hit enter.
5. Select the rail curves. Maya will create a NURBS surface that looks a little like a hill with varying heights depending on the rider curves you made.

Once I finish these steps.. the Command Feedback always says: Error: mpBirailSrf2 (Mp Birail Srf Node): birail surface computation failed

What could be the problem?... if you need more info or images of my problem just ask.. Sorry for not posting them now if you need to see them.