How to reproduce: Change the current culture so that a comma is used as a decimal separator, the Elevations example will fail with a (400) Bar Request error.

Workaround: create a custom BingRestMapProvider class
public class CustomBingRestMapProvider : BingRestMapProvider
    {
        protected override string GetPointsString(List<PointG> points)
        {
            StringBuilder sb = new StringBuilder();

            for (int i = 0; i < points.Count; i++)
            {
                PointG point = points[i];

                if (i > 0)
                {
                    sb.Append(",");
                }

                sb.Append(point.Latitude.ToString(CultureInfo.InvariantCulture) + "," + point.Longitude.ToString(CultureInfo.InvariantCulture));
            }

            return sb.ToString();
        }
    }