//Header file
using System.Data;
using System.Data.SqlClient;
using System.Configuration;



public Form3()
    {
        InitializeComponent();

        //string cs = Properties.Settings.TestDatabaseConnectionString;
        var connectionString = ConfigurationManager.ConnectionStrings["TestDatabaseConnectionString"].ConnectionString;

        using (SqlConnection con = new SqlConnection())
        {
            con.ConnectionString = connectionString;

            SqlCommand cmd = new SqlCommand();
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.CommandText = "ReportStudentDetails";
            cmd.Connection = con;

            con.Open();
            SqlDataAdapter sda = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            sda.Fill(ds);

            gridControl1.DataSource = ds;
            gridControl1.DataBind(); // showing error
            con.Close();

        }

    }