序列化问题BinaryFormatter


 protected void Button1_Click(object sender, EventArgs e)
        {
            List<object> listobj=new List<object>();
            listobj.Add("111");
            listobj.Add(111111111);            
            BinaryFormatter ser = new BinaryFormatter();
            MemoryStream ms = new MemoryStream();
            ser.Serialize(ms, listobj);
            byte[] bt = ms.ToArray();
            ViewState["bt"] = System.Text.Encoding.UTF8.GetString(bt);
        }        protected void Button2_Click(object sender, EventArgs e)
        {
            if (ViewState["bt"]!=null)
            {
                byte[] ch = new byte[1024];
                ch = System.Text.Encoding.UTF8.GetBytes(ViewState["bt"].ToString());
                MemoryStream ms = new MemoryStream(ch);
                //ms.Seek(0
                BinaryFormatter ser = new BinaryFormatter();
                List<object> listobj=(List<object>)ser.Deserialize(ms);
                Response.Write(listobj.Count);            }
        }
有错误  不知道怎么解决