error in this below code

See more:

C#

i have error inthis code that error is(The connection name 'ConnectionString' was not found in the applications configuration or the connection string is empty.)

Line 48: </Columns>
Line 49: </asp:GridView>
Line 50: <asp:SqlDataSource ID="SqlDataSource1" runat="server"
Line 51: ConnectionString="<%$ ConnectionStrings:ConnectionString %>"
Line 52: SelectCommand="SELECT [ID], [ImageName], [Image]

(but am using sql local server windows authenticatation in that there is no userid and passwor)

using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Configuration;
using System.Data.SqlClient;
using System.Data;

public partial class fileupload : System.Web.UI.Page
{
    
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void btnUpload_Click(object sender, EventArgs e)
    {
        string strImageName = txtName.Text.ToString();
        if (FileUpload1.PostedFile != null &&
            FileUpload1.PostedFile.FileName != "")
        {
            byte[] imageSize = new byte
                          [FileUpload1.PostedFile.ContentLength];
            HttpPostedFile uploadedImage = FileUpload1.PostedFile;
            uploadedImage.InputStream.Read
               (imageSize, 0, (int)FileUpload1.PostedFile.ContentLength);

            // Create SQL Connection 
            SqlConnection con = new SqlConnection("server=USER\\SQLEXPRESS;user id=;password;database=images");
            con.ConnectionString = ConfigurationManager.ConnectionStrings
                                   ["ConnectionString"].ConnectionString;

            // Create SQL Command 

            SqlCommand cmd = new SqlCommand();
            cmd.CommandText = "INSERT INTO Images(ImageName,Image)" +
                              " VALUES (@ImageName,@Image)";
            cmd.CommandType = CommandType.Text;
            cmd.Connection = con;

            SqlParameter ImageName = new SqlParameter
                                ("@ImageName", SqlDbType.VarChar, 50);
            ImageName.Value = strImageName.ToString();
            cmd.Parameters.Add(ImageName);

            SqlParameter UploadedImage = new SqlParameter
                          ("@Image", SqlDbType.Image, imageSize.Length);
            UploadedImage.Value = imageSize;
            cmd.Parameters.Add(UploadedImage);
            con.Open();
            int result = cmd.ExecuteNonQuery();
            con.Close();
            if (result > 0)
                lblMessage.Text = "File Uploaded";
            GridView1.DataBind();


        }
    }
}
<%@ WebHandler Language="C#" Class="Handler" %>

using System;
using System.Web;
using System.Configuration;
using System.Data.SqlClient;



public class Handler : IHttpHandler {
    
    public void ProcessRequest (HttpContext context) {
        SqlConnection con = new SqlConnection("server=USER\\SQLEXPRESS;user id=;password;database=images");
        con.ConnectionString = ConfigurationManager.ConnectionStrings
                              ["ConnectionString"].ConnectionString;
        // Create SQL Command 
SqlCommand cmd = new SqlCommand();
cmd.CommandText = "Select ImageName,Image from Images" + 
                  " where ID =@ID";
cmd.CommandType = System.Data.CommandType.Text;
cmd.Connection = con;

SqlParameter ImageID = new SqlParameter
                    ("@ID", System.Data.SqlDbType.Int);
ImageID.Value = context.Request.QueryString["ID"];
cmd.Parameters.Add(ImageID);
con.Open();
SqlDataReader dReader = cmd.ExecuteReader();
dReader.Read();
context.Response.BinaryWrite((byte[])dReader["Image"]);
dReader.Close();
con.Close();
}


    
 
    public bool IsReusable {
        get {
            return false;
        }
    }

}