Exception with GetPointAtDist

csharp

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Autodesk.AutoCAD.Geometry;
using AcBr = Autodesk.AutoCAD.BoundaryRepresentation;
using Autodesk.AutoCAD.Runtime;

namespace Autodesk.AutoCAD.DatabaseServices
{
   public static class PolylineExtensionMethods
   {
      /// <summary>
      ///
      /// Returns true if the given Polyline forms a
      /// closed boundary and its Closed property is
      /// false.
      ///
      /// The result is true if any of the
      /// following conditions are true:
      ///
      /// 1.  Any segment intersects any other segment.
      ///      Regardless of the value of the Closed property.
      ///
      /// 2.  Any vertex lies directly on any segment.
      ///     or is coincident with any other vertex,
      ///     including zero-length segments, regardless
      ///     of the value of the Closed property
      ///
      /// 3.  If the first and last vertices are coincident,
      ///     AND the PolyLine's Closed property is false,
      ///     the polyline is considered effectively closed.
      ///     
      ///  4. A Closed polyline with < 3 vertices.
      ///     
      /// The test is intended to be consistent with the
      /// REGION command's testing of boundary entities.
      ///     
      /// </summary>

      public static bool IsEffectivelyClosed( this Polyline pline )
      {
         int numverts = pline.NumberOfVertices;
         if( numverts < 3 )
            return pline.Closed;

         if( !pline.Closed && pline.StartPoint.IsEqualTo( pline.EndPoint ) )
            return true;

         Point3dCollection points = new Point3dCollection();

         pline.IntersectWith( pline, Intersect.OnBothOperands, points,
            IntPtr.Zero, IntPtr.Zero );

         if( !pline.Closed )
            numverts -= 2;

         return points.Count != numverts;
      }
   }
}