为什么阅读器关闭了

 StringBuilder AdminNav = new StringBuilder();
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            OleDbConnection MyConn;
            MyConn = new OleDbConnection(ConfigurationManager.AppSettings["myconnstring"].ToString() + System.Web.HttpContext.Current.Server.MapPath(ConfigurationManager.AppSettings["mydbpath"]));
            MyConn.Open();
            string cmdText = "SELECT * FROM AdminMenu";
            OleDbCommand Mycommend = new OleDbCommand(cmdText, MyConn);
            OleDbDataReader Myreader;
            Myreader = Mycommend.ExecuteReader();
            while (Myreader.Read())
            {
                AdminNav.Append("<dl><dt class=menu2 onmouseup=opencat(cat"+Myreader["NavId"].ToString()+",img"+Myreader["NavId"].ToString()+");><img id=img"+Myreader["NavId"].ToString()+" src=../images/class1.gif>&nbsp;"+Myreader["Name"].ToString()+"</dt><dd id=cat"+Myreader["NavId"].ToString()+" style='display:none;'><ul>");                string cmdText2 = "select * from AdminMenu where NavParentId=" + Myreader["NavId"].ToString() + " and IsShow=true ";
                OleDbCommand Mycommend2=new OleDbCommand(cmdText2,MyConn);
                OleDbDataReader Myreader2;
                Myreader2=Mycommend2.ExecuteReader();     //为什么这个reader读不出来，哪里关闭了？
                while (Myreader2.Read())
                {
                    AdminNav.Append("<li><a href=../"+Myreader2["Folder"].ToString()+"/"+Myreader2["Href"].ToString()+">"+Myreader2["Name"].ToString()+"</a></li>");
                    Myreader2.Close();
                }
                AdminNav.Append("</ul></dd></dl>");
            }
            //Myreader.Close();
           AdminNavlist.Text=AdminNav.ToString();   
        }    }为什么会出错，阅读器关闭时 Read 的尝试无效。
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