Problemacon mysql y php

[LuZBinG]

no sera por esto:

include ('BOOK_SC_FNS.php');
session_start();

--------$isbn=$_GET['isbn'];//te falta esto---------------------
$book = get_book_details($isbn);
do_html_header($book["title"]);
display_book_details($book);
$target = "index.php";