Invalid attempt to call Read when reader is closed.

Got an Error when i am using DataReader. Code which i am using is below:-
string fetch_isbn = "Select * From rt_cartdetail where cartdetail_cartid='" + Session["cart_pid"] + "'";
SqlCommand objcmd_ISBN = new SqlCommand(fetch_isbn, objconn);
objconn.Open();
{
//CommandBehavior.CloseConnection
SqlDataReader reader_isbn = (SqlDataReader)objcmd_ISBN.ExecuteReader(CommandBehavior.CloseConnection);
if (reader_isbn != null && reader_isbn.HasRows)
{
while (reader_isbn.Read())
{
string isbn = reader_isbn["cartdetail_isbn"].ToString();
int qty = Convert.ToInt32(reader_isbn["cartdetail_qty"]);
reader_isbn.NextResult();
objconn.Close();
//Response.Redirect(isbn);
string fetch_sell_book_details = "Select * From sell_book where product_id='" + isbn + "'";
SqlCommand objcmd_sell_book_details = new SqlCommand(fetch_sell_book_details, objconn);
objconn.Open();
{
Sql ...