I am using this code for fetch all the data when select any item of dropdownbox using three tier technique,in asp.net.

program:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Data;
using System.Data.SqlClient;
using System.Web.UI.WebControls;
using Fobbs.Logic;
using System.Globalization;
using System.Threading.Tasks;

namespace Fobbs
{
    public partial class Eng1 : System.Web.UI.Page
    {
        IndexLogic il = new IndexLogic();
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                Aieebind();

            }
        }

        void Aieebind()
        {
            DataSet ds = new DataSet();
            ds = il.FetchData(1);
            DDLAieee.DataSource = ds.Tables[0];
            DDLAieee.DataBind();
            DDLAieee.Items.Insert(0, new ListItem("Select", "Select"));
        }


        protected void DDLAieee_SelectedIndexChanged(object sender, EventArgs e)
        {
            DataSet ds = new DataSet();
            ds = il.FetchDataById(2,DDLAieee.SelectedItem.Value);
 
    
            if (ds.Tables[0].Rows.Count > 0)
            {
                txtdescription.Text = ds.Tables[0].Rows[0][1].ToString();
                
            }
        }
    }
}

ds = il.FetchDataById(2,DDLAieee.SelectedItem.Value);

Input string was not in a correct format.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.FormatException: Input string was not in a correct format.

Source Error:


Line 38:         {
Line 39:             DataSet ds = new DataSet();
Line 40:             ds = il.FetchDataById(2, Convert.ToInt32(DDLAieee.SelectedItem.Text));
Line 41: 
Line 42:             if (ds.Tables[0].Rows.Count > 0)


Source File: C:\Users\ADI\Documents\Visual Studio 2010\Projects\Fobbs\Fobbs\Eng1.aspx.cs    Line: 40