how to solve for namespace name 'OracleBulkCopy' could not be found issue ?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.IO;
using Microsoft.VisualBasic;
using System.Collections;
using System.Data;
using System.Diagnostics;
using System.Configuration;
using System.Text;
using System.Data.OleDb;
using System.Data.OracleClient;

//using Oracle.DataAccess;
//using Oracle.DataAccess.Client;


					{
                                            OracleConnection objConnection = new OracleConnection(System.Configuration.ConfigurationManager.ConnectionStrings["Connection"].ConnectionString);
                                                objConnection.Open();
                                                using (OracleTransaction OracleTransaction = objConnection.BeginTransaction())
                                                {
                                                    using (OracleBulkCopy OracleBulkCopy = new OracleBulkCopy(objConnection, OracleBulkCopyOptions.Default, OracleTransaction))
                                                    {
                                                        OracleBulkCopy.DestinationTableName = "OP_TTP_TBL";

                                                        OracleBulkCopy.ColumnMappings.Add("CONTACT_NAME", "CONTACT_NAME");
                                                        OracleBulkCopy.ColumnMappings.Add("APP_NAME", "APP_NAME");

                                                            OracleBulkCopy.WriteToServer(dt);
                                                            OracleTransaction.Commit();

                                                    }
                                                }
                                                objConnection.Close();
                                        } 

My code as above with the reference I using in my page, but I always hit error 'The type or namespace name 'OracleBulkCopy' could not be found (are you missing a using directive or an assembly reference?)

Anyone know how to resolve of this? try to search from Google and tested many way also same..

If I added //using Oracle.DataAccess;    
//using Oracle.DataAccess.Client;

it will showing "Could not load file or assembly 'Oracle.DataAccess' or one of its dependencies. An attempt was made to load a program with an incorrect format."