Splines can sometimes have unintentional twisting between spline points. The control points may have the correct rotation, but the default spline can twist leaving a spline mesh that looks like its tied in a knot. This is especially true when the up vector at a spline point rotates more than 90 degrees.

This plugin has several functions which aid in building a new spline that will result in a smooth untwisted spline from a user generated spline. Please download the Sample Project in the link below to understand how all these functions go together.