C# Class Library in WCF Service Application

I have a problem with C# class library and WCF Service Application. I built a class library with two classes Graph and Vertice. And they have few public methods inside. Then I created and published(IIS 7) a simple WCF Application, which uses this class library. Code:

public class GraphsService : IGraphsService
{
    public Graph getGraph(int val)
    {
        return new Graph(val);
    }
}

Of course publish process went fine, and I have an access to this WCF. And now the problem:

When I created an Client Application(Web) and added service reference to this project, I can access the method getGraph(int val) but it returns class which doesn't have any of the methods I implemented in class library. Code for client:

protected void Page_Load(object sender, EventArgs e)
    {
        GraphsServiceClient gc = new GraphsServiceClient();
        Graph g = gc.getGraph(5);
        lblGraph.Text = g.ToString();
    }

That line returns me

GraphsClient.GraphService.Graph

But I want it to return my overriden method ToString(which is implemented in class library). How can I make it works?'

My Graph class from Class Library(removed few methods:

public class Graph
    {
        protected List<Vertice> _vertices;

        public Graph()
        {
            this._vertices = new List<Vertice>();
        }
        public Graph(int startValue)
        {
            this._vertices = new List<Vertice>();
            this._vertices.Add(new Vertice(startValue));
        }

        public List<Vertice> Vertices
        {
            get
            {
                return this._vertices;
            }
        }

        public Vertice getFirstVertice()
        {
            if (this._vertices.Count != 0) return this._vertices.First();
            throw new GraphException("Graaph doesn't have any vertices in it!");
        }

        public Vertice findVertice(int value)
        {
            foreach (Vertice v in this._vertices)
            {
                if (v.value == value) return v;
            }
            return null;
        }

        public Graph addVertice(Vertice v, bool undirected = true)
        {
            if (this._vertices.Contains(v)) throw new GraphException("There is already this vertice in graph!");
            foreach (int val in v.Neighbours)
            {
                Vertice tmp = this.findVertice(val);
                if (tmp != null)
                {
                    if (undirected) tmp.addNeighbour(v.value);
                }
                else throw new GraphException("There isn't a vertice " + val + " in graph so it can't be in neighbours list!");
            }
            this._vertices.Add(v);
            return this;
        }

        public int[,] getAdjacencyMatrix()
        {
            int[,] adMatrix = new int[this._vertices.Count + 1, this._vertices.Count + 1];
            Array.Clear(adMatrix, 0, adMatrix.Length);
            int l = 1;
            foreach (Vertice v in this._vertices)
            {
                adMatrix[0, l] = v.value;
                adMatrix[l, 0] = v.value;
                l++;
            }
            for (int i = 1; i < this._vertices.Count + 1; i++)
            {
                for (int j = 1; j < this._vertices.Count + 1; j++)
                {
                    int val1 = adMatrix[i, 0];
                    int val2 = adMatrix[0, j];
                    Vertice v = this.findVertice(val1);
                    if (v.hasNeighbour(val2)) adMatrix[i, j] = v.countNeighbours(val2);
                }
            }
            return adMatrix;
        }

        public string getAdjacencyMatrixAsString()
        {
            string ret = "";
            int[,] adM = this.getAdjacencyMatrix();
            for (int i = 0; i < Math.Sqrt((double)adM.Length); i++)
            {
                for (int j = 0; j < Math.Sqrt((double)adM.Length); j++)
                {
                    if (i != 0 || j != 0) ret += adM[i, j] + "\t";
                    else ret += "\t";
                }
                ret += "\n";
            }
            return ret;
        }

        public override string ToString()
        {
            string ret = "";
            foreach (Vertice v in this._vertices)
            {
                ret += "Vertice: " + v.value + " neighbours: ";
                foreach (int val in v.Neighbours)
                {
                    ret += val + ", ";
                }
                ret = ret.Remove(ret.Length - 2);
                ret += "\n";
            }
            ret = ret.Remove(ret.Length - 1);
            return ret;
        }

    }

Copyright Notice：Content Author:「Michał Świątek」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/30036752/c-sharp-class-library-in-wcf-service-application