ExecuteScalar 要求已打开且可用的连接。连接的当前状态为已关闭

问题是：我已经在每次用完DataReader后，都把对应的DataReader关闭了，同时他们共用一个SqlConnection，不过我每次用时，都把CommandText改过来了，可是还是出现这个错误提示，请高手指点。
this.Exsql.Open();
            string cmdText = "";
            string text2 = "";
            string text3 = "";
            string text4 = "";
            string text5 = "";
            cmdText = "select DISTINCT YX_ProID from YX_Shoping";
            SqlCommand com = new SqlCommand(cmdText, this.Exsql.con);
            SqlDataReader reader = com.ExecuteReader();
            DataSet set = new DataSet();
            DataTable table = new DataTable("tab1");
            set.Tables.Add(table);
            DataColumn column = new DataColumn("YX_ID", Type.GetType("System.Int32"));
            set.Tables["tab1"].Columns.Add(column);
            column = new DataColumn("YX_ProName", Type.GetType("System.String"));
            set.Tables["tab1"].Columns.Add(column);
            column = new DataColumn("YX_ProNum", Type.GetType("System.Int32"));
            column.DefaultValue = 0;
            set.Tables["tab1"].Columns.Add(column);
            column = new DataColumn("YX_ProPic", Type.GetType("System.String"));
            set.Tables["tab1"].Columns.Add(column);            int Lenreader = -1;
            Hashtable hashtable = new Hashtable();
            
            while (reader.Read())
            {
                Lenreader++;   
                hashtable.Add(Lenreader, reader[0].ToString());
                      
            }
            reader.Close();            for (int i = 0; i <= Lenreader;i++ )
            {
                com.CommandText="Select sum(YX_OrderProNum) from YX_Shoping where YX_ProID='" + hashtable[i].ToString() + "'";
                int num = Convert.ToInt32(com.ExecuteScalar());
                com.CommandText="Select YX_ProID,YX_ProName from YX_Shoping where YX_ProID='" + hashtable[i].ToString() + "'";
                SqlDataReader reader2 = com.ExecuteReader();
                string text8 = "";
                string text9 = "";
                int num2 = 0;
                if (reader2.Read())
                {
                    text8 = reader2["YX_ProName"].ToString();
                    num2 = Convert.ToInt16(reader2[0].ToString());
                }
                string Insreader2 = reader2[0].ToString();
                reader2.Close();
                com.CommandText="select YX_Spic from YX_Product where YX_ID=" + Convert.ToInt16(Insreader2);
                SqlDataReader reader3 = com.ExecuteReader(CommandBehavior.CloseConnection);
                if (reader3.Read())
                {
                    text9 = reader3[0].ToString();
                }
               
                DataRow row = table.NewRow();
                row[0] = num2;
                row[1] = text8;
                row[2] = num;
                row[3] = text9;
                table.Rows.Add(row); reader3.Close();
            }
            
            table.DefaultView.Sort = "YX_ProNum desc";
            DataRowCollection rows = table.Rows;
            int count = table.Rows.Count;
            if (count != 0)
            {
                text2 = rows[0]["YX_ProPic"].ToString();
                text3 = rows[0]["YX_ID"].ToString();
                text4 = rows[0]["YX_ProName"].ToString();
                if (text3 == "")
                {
                    text3 = "0";
                }
                int num4 = 1;
                for (int i = 1; i < count; i++)
                {
                    if (num4 >= 10)
                    {
                        break;
                    }
                    string text11 = text5;
                    text5 = text11 + "<TR><TD bgColor='#cccccc' colSpan='2' height=1></TD></TR>\n<TR>\n<TD onmouseover=\"this.style.backgroundColor='#EDEBEF'\" style=\"CURSOR:' hand'; HEIGHT: '21px'; BACKGROUND-COLOR: '#ffffff'\" onmouseout=\"this.style.backgroundColor='#FFFFFF'\" align=left colSpan=2 height=21>\n<a href={$Hope_SitUrl$}ShowProduct.aspx?YX_MID=" + rows[i]["YX_ID"].ToString() + " style='color:#676767'>" + newstr(rows[i]["YX_ProName"].ToString(), 12) + "</a>\n</TD></TR>\n";
                    num4++;
                }
            }
            this.Exsql.Close(); public class YX_sql
    {
        public SqlConnection con;
        public YX_sql()
        {
            this.con = new SqlConnection(System.Configuration.ConfigurationSettings.AppSettings["YXPath"]);
        }
}