Having trouble creating a sweep

Hi everyone,

I am trying to create a sweep from a line, but when I do this eyeshot gives the following error: "Invalid plane definition."

The curve I am trying to make a sweep from looks as follows:

The curve is a single curve with 3 degrees and 97 control points.

I am following an example to create the sweep. This is my code:

var lineToFollow = new CompositeCurve(ViewModel.SelectedCurves);
var plane = new Plane(lineToFollow.StartPoint, lineToFollow.StartTangent);
var profile = new Ellipse(plane, lineToFollow.StartPoint, 2, 2);
var sweep = profile.SweepAsSurface(lineToFollow, 0);

MainDesign.Entities.AddRange(sweep);

Does anyone know why this error is thrown, and how I can resolve this? Thanks in advance!