如何解决反序列化中的此错误？

sCreator.exe中发生了类型为'System.InvalidCastException'的未处理异常。其他信息：无法将类型为'System.String'的对象转换为类型为'sCreator.Shape'。

这是代码：

    public void Deseriaize(StreamReader file)
    {
        XmlSerializer ser = new XmlSerializer(typeof(string));
        Shape s = (Shape)ser.Deserialize(file);
        file.Close();
        MessageBox.Show(s.title);
    }

    private void btn_OpenProject_Click(object sender, EventArgs e)
    {
        StreamReader file = new StreamReader(@"C:\Users\pb8n0053\Documents\SerializationOverview.seal");
        Deseriaize(file);
    }

形状等级

 [Serializable]
public class Shape
{
    //Properties
    public Draw draw;
    public String title;
    public float width { get; set; }
    public float height { get; set; }
    public float x { get; set; }
    public float y { get; set; }
    public static PointF center = new PointF(250f, 250f);
    public int strokeThickness { get; set; }
    public Color color { get; set; }
    public float userDefinedWidth { get; set; }
    public float userDefinedHeight { get; set; }
    public int userDefinedStroke { get; set; }
    public SizeF size;
    public PointF location;
    public float radius;
    public ShapeType type;
    public Status status;
    public enum ShapeType
    {
        rectangle, square, circle, ellipse, triangle, image
    }
    public enum Status
    {
        editing, start
    }
}