I need help with path hexagon

I've been following this tutorial "http://tbswithunity3d.wordpress.com/" and now I'm getting this error:

Assets/ForceX Hex Grid/Scripts/Path.cs(7,14): error CS0535: `Path' does not implement interface member `System.Collections.IEnumerable.GetEnumerator()'

Could anyone help me, I'm new to C#. I have never worked with objective oriented code before, I've worked with HTML and PHP. Now I'm working with a couple of friends with a turn based HexGrid game and we really need some help.

Thanks in advanced for anyone who takes the time to reply!

 using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 
 public class Path: IEnumerable
 {
 class Path<Node> : IEnumerable<Node>
         {
        public Node LastStep { get; private set; }
     public Path<Node> PreviousSteps { get; private set; }
     public double TotalCost { get; private set; }
     public Path(Node lastStep, Path<Node> previousSteps, double totalCost)
         {
         LastStep = lastStep;
         PreviousSteps = previousSteps;
         TotalCost = totalCost;
         }
     public Path(Node start) : this(start, null, 0) {}
     public Path<Node> AddStep(Node step, double stepCost)
         {
         return new Path<Node>(step, this, TotalCost + stepCost);
         }
     public IEnumerator<Node> GetEnumerator()
         {
         for (Path<Node> p = this; p != null; p = p.PreviousSteps)
             yield return p.LastStep;
         }
         
     IEnumerator IEnumerable.GetEnumerator()
         { 
         return this.GetEnumerator();
         }
         }
 }