Upload Multiple Files Asynchronously Using AJAX into SQL Server Database

Am trying to upload multiple file to database, but getting error

This is my .aspx file

<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true"
    CodeBehind="Default.aspx.cs" Inherits="AJAXFileUploadSQL._Default" %><%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="ajaxToolkit" %><asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent"><style>
        .ajax__fileupload_button
        {
            background-color: blue;
        }</style><script type="text/javascript">
        function onClientUploadComplete(sender, e) {
            var id = e.get_fileId();
            onImageValidated("TRUE", e);
        }

        function onImageValidated(arg, context) {

            var test = document.getElementById("testuploaded");
            test.style.display = 'block';

            var fileList = document.getElementById("fileList");
            var item = document.createElement('div');
            item.style.padding = '4px';

            if (arg == "TRUE") {
                var url = context.get_postedUrl();
                url = url.replace('&amp;', '&');
                item.appendChild(createThumbnail(context, url));
            } else {
                item.appendChild(createFileInfo(context));
            }

            fileList.appendChild(item);

        }

        function createFileInfo(e) {
            var holder = document.createElement('div');
            holder.appendChild(document.createTextNode(e.get_fileName() + ' with size ' + e.get_fileSize() + ' bytes'));

            return holder;
        }

        function createThumbnail(e, url) {
            var holder = document.createElement('div');
            var img = document.createElement("img");
            img.style.width = '80px';
            img.style.height = '80px';
            img.setAttribute("src", url);

            holder.appendChild(createFileInfo(e));
            holder.appendChild(img);

            return holder;
        }
    </script></asp:Content><asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent"><h2>
        Upload Files Asynchronously Using AJAX into SQL Server Database</h2><br /><ajaxToolkit:ToolkitScriptManager runat="Server" EnablePartialRendering="true" ID="ScriptManager1" /><div><asp:Label runat="server" ID="myThrobber" Style="display: none;"><img align="absmiddle" alt="" src="uploading.gif"/></asp:Label><ajaxToolkit:AjaxFileUpload ID="AjaxFileUpload1" runat="server" padding-bottom="4"
            padding-left="2" padding-right="1" padding-top="4" ThrobberID="myThrobber" OnClientUploadComplete="onClientUploadComplete"
            OnUploadComplete="AjaxFileUpload1_OnUploadComplete" /><br /><div id="testuploaded" style="display: none; padding: 4px; border: gray 1px solid;"><h4>
                Uploaded files:</h4><hr /><div id="fileList"></div></div></div></asp:Content>

My CS File

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;
using System.Collections.Specialized;
using System.Text;
using System.IO;
using System.Linq;
using AjaxControlToolkit;

namespace AJAXFileUploadSQL
{
    public partial class _Default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            String strConnString = ConfigurationManager.ConnectionStrings["Con"].ConnectionString;
            SqlConnection _con = new SqlConnection(strConnString);

            if (Request.QueryString["preview"] == "1" && !string.IsNullOrEmpty(Request.QueryString["fileId"]))
            {
                var fileId = Request.QueryString["fileId"];
                var fileContentType = (string)Session["fileContentType_" + fileId];
                var fileName = (string)Session["fileName_" + fileId];
                byte[] imageBytes = File.ReadAllBytes(System.Web.HttpContext.Current.Server.MapPath("~") + "file.png");
                var fileContents = imageBytes;

                string ct = (string)Session["fileContentType_" + fileId];
                if (ct.Contains("jpg") || ct.Contains("gif") || ct.Contains("png") || ct.Contains("jpeg"))
                    fileContents = (byte[])Session["fileContents_" + fileId];

                //using (SqlConnection _con = new SqlConnection("Data Source=ASHRAF-PC;database=AJAXFileUploadSQL;User Id=sa;Password=sa@1;MultipleActiveResultSets=True"))



                using (SqlCommand _cmd = new SqlCommand("UploadFile", _con))
                {
                    _cmd.CommandType = CommandType.StoredProcedure;
                    _cmd.Parameters.AddWithValue("@FileName", fileName);
                    _cmd.Parameters.AddWithValue("@FileType", fileContentType);
                    _cmd.Parameters.AddWithValue("@FileContent", (byte[])Session["fileContents_" + fileId]);

                    _con.Open();
                    _cmd.ExecuteNonQuery();
                    _con.Close();
                }

                Response.Clear();
                Response.ContentType = fileContentType;
                Response.BinaryWrite(fileContents);
                Response.End();
            }
        }

        public byte[] imageToByteArray(System.Drawing.Image imageIn)
        {
            MemoryStream ms = new MemoryStream();
            imageIn.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
            return ms.ToArray();
        }

        protected void AjaxFileUpload1_OnUploadComplete(object sender, AjaxFileUploadEventArgs file)
        {
            Session["fileContentType_" + file.FileId] = file.ContentType;
            Session["fileContents_" + file.FileId] = file.GetContents();

            Session["fileName_" + file.FileId] = file.FileName.Split('\\').Last();

            file.PostedUrl = string.Format("?preview=1&fileId={0}", file.FileId);
        }
    }
}

Don't know where is the error