You see the example below why the error not found namespace or class ?

[url]http://www.mediafire.com/file/iiak7w5nhhab3ju/Namespace_asp_net.rar/file[/url]

Can you please post your code here? The page you linked to seems very spammy.

code here

file ChitietSP.aspx.cs

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.Diagnostics;               // Debug
//using connectSQL;
//using ROOT_Namespace.connectSQL;

    public partial class _Default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                LoadData();
            }
        }

        string sSQL;
        private void LoadData()
        {

            sSQL = "SELECT NGAY, MASOPHIEU, KHACHDUA, TONGTIEN, TONGTHU, TENKH, TEL, ADRESS, GIAM, DOITRA, TTTHANHTOAN, THANHTOAN, MANHANVIEN, NHANVIEN ";
            sSQL += "FROM TABKHACHHANGNOCTTMP ";
            sSQL += "ORDER BY MASOPHIEU;";
            Debug.Print("sSQL: " + sSQL.ToString());
            //DataTable dtKhachNoTmp = clsConnecACS.FillDatatable(sSQL);
            //ClsConnecSQL abc = new ClsConnecSQL();
            //GridView1.DataSource = abc.FillDatatable(sSQL);
            GridView1.DataSource = ClsConnecSQL.FillDatatable(sSQL);
        }

        private void LoadData(string tenNhanVien)
        {
            sSQL = "SELECT NGAY, MASOPHIEU, KHACHDUA, TONGTIEN, TONGTHU, TENKH, TEL, ADRESS, GIAM, DOITRA, TTTHANHTOAN, THANHTOAN, MANHANVIEN, NHANVIEN ";
            sSQL += "FROM TABKHACHHANGNOCTTMP ";
            sSQL += "WHERE TABKHACHHANGNOCTTMP.TEN = N'" + tenNhanVien + "' ";
            sSQL += "ORDER BY MASOPHIEU;";
            Debug.Print("sSQL: " + sSQL.ToString());

            GridView1.DataSource = ClsConnecSQL.FillDatatable(sSQL);
        }

        protected void btnSearch_Click(object sender, System.EventArgs e)
        {
            if (string.IsNullOrEmpty(txtSearch.Text))
            {
                lblMessage.ForeColor = System.Drawing.Color.Red;
                lblMessage.Text = "Nhập [Tên nhân viên] cần tìm";
            }
            else
            {
                lblMessage.Text = "";
                LoadData(txtSearch.Text.Trim());
            }
        }
    }

file clsConnecSQL.cs

using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Drawing;        
using System.Diagnostics;    
using System.Data.SqlClient; 
//using System.Windows.Forms;  
using System.Configuration;  

//using connectSQL;

namespace connectSQL //System.Web.UI.Page //
{
    public class ClsConnecSQL
    {

        public static DataTable FillDatatable(string sSQL)
        {
            string connectionString = "Server=MICROSOFT;uid=sa;pwd=123456;database=NhaDat";
            SqlConnection sqlConn = new SqlConnection(connectionString);
            sqlConn.Open();
            DataTable dataTable = new DataTable();
            SqlDataAdapter adapter = new SqlDataAdapter(sSQL, sqlConn);
            adapter.Fill(dataTable);

            return dataTable;
        }

        //public static DataTable Plus(int a, int B)/>/>
        //{
        //    return a + b;
        //}

    }   
}