using system.data.sqlclient;中的SYSTEM找不到类型或命名空间名称“system”(是否缺少 using 指令或程序集引用?)

Question

错误 2 找不到类型或命名空间名称“system”(是否缺少 using 指令或程序集引用?)  我将所有代码粘贴出来，高手帮忙看看 VS2008环境下

using System;

using System.Collections;

using System.Configuration;

using System.Data;

using System.Linq;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.HtmlControls;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Xml.Linq;

using system.data.Sqlclient;



namespace WebApplication2

{

    public partial class WebForm1 : System.Web.UI.Page

    {

        protected void Page_Load(object sender, EventArgs e)

        {

            string username = Request.Form["username"];

            string userPWD= Request.Form["username"];

            sqlconnection con = sqlconnection("sever=.;database=database;");

            con.open();

            sqlcommand cmd = new sqlcommand("select count(*) from admin where name='" + username + "'and pwd='" + userPWD + "' ");

            int count = Convert.ToInt32(cmd.executescalar());

            if (count > 0)

            {

                Response.Redirect("main.aspx");

            }

            else

            {

                Response.Redirect("loginfail.htm");

            }

        }

    }

}

Answer 1

system大写

System

c#严格区分大小写

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【孟子E章】

Answer 2

using System.Data.SqlClient;

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【孟子E章】