Trouble with Graph Data Structure C#

I've just started learning how to program and have been following along with this tutorial on graphs but I've run into some issues using the given

AddDirectedEdge(GraphNode<T> from, GraphNode<T> to, int cost)

It fails to build using the default from the tutorial, for example

web.AddDirectedEdge("People.aspx", "Privacy.htm");  // People -> Privacy

This gives the error "No overload for method 'AddDirectedEdge' takes 2 arguments". Adding an integer as a third argument does not help either, it just gives another error "Argument#: cannot convert from 'string' to 'GraphTest.GraphNode< string>'"

I'm not sure how to fix this, any help/insight regarding it would be appreciated. For ease of viewing the graph and graph node classes are shown below (these are all available through the above link as well):

 public class GraphNode<T> : Node<T>
{
    private List<int> costs;

    public GraphNode() : base() { }
    public GraphNode(T value) : base(value) { }
    public GraphNode(T value, NodeList<T> neighbors) : base(value, neighbors) { }

    new public NodeList<T> Neighbors
    {
        get
        {
            if (base.Neighbors == null)
                base.Neighbors = new NodeList<T>();

            return base.Neighbors;
        }
    }

    public List<int> Costs
    {
        get
        {
            if (costs == null)
                costs = new List<int>();

            return costs;
        }
    }
}

.

 public class Graph<T> : IEnumerable<T>
{
    private NodeList<T> nodeSet;

    public Graph() : this(null) { }
    public Graph(NodeList<T> nodeSet)
    {
        if (nodeSet == null)
            this.nodeSet = new NodeList<T>();
        else
            this.nodeSet = nodeSet;
    }

    public void AddNode(GraphNode<T> node)
    {
        // adds a node to the graph
        nodeSet.Add(node);
    }

    public void AddNode(T value)
    {
        // adds a node to the graph
        nodeSet.Add(new GraphNode<T>(value));
    }

    public void AddDirectedEdge(GraphNode<T> from, GraphNode<T> to, int cost)
    {
        from.Neighbors.Add(to);
        from.Costs.Add(cost);
    }

    public void AddUndirectedEdge(GraphNode<T> from, GraphNode<T> to, int cost)
    {
        from.Neighbors.Add(to);
        from.Costs.Add(cost);

        to.Neighbors.Add(from);
        to.Costs.Add(cost);
    }

    public bool Contains(T value)
    {
        return nodeSet.FindByValue(value) != null;
    }

    public bool Remove(T value)
    {
        // first remove the node from the nodeset
        GraphNode<T> nodeToRemove = (GraphNode<T>)nodeSet.FindByValue(value);
        if (nodeToRemove == null)
            // node wasn't found
            return false;

        // otherwise, the node was found
        nodeSet.Remove(nodeToRemove);

        // enumerate through each node in the nodeSet, removing edges to this node
        foreach (GraphNode<T> gnode in nodeSet)
        {
            int index = gnode.Neighbors.IndexOf(nodeToRemove);
            if (index != -1)
            {
                // remove the reference to the node and associated cost
                gnode.Neighbors.RemoveAt(index);
                gnode.Costs.RemoveAt(index);
            }
        }

        return true;
    }

    public NodeList<T> Nodes
    {
        get
        {
            return nodeSet;
        }
    }

    public int Count
    {
        get { return nodeSet.Count; }
    }

    public IEnumerator<T> GetEnumerator()
    {
        throw new NotImplementedException();
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        throw new NotImplementedException();
    }

    IEnumerator<T> IEnumerable<T>.GetEnumerator()
    {
        throw new NotImplementedException();
    }
}