PHP button returns 404 Error-php Tutorial

The PHP button returns the content in the 404 error book, and the database and login. PHP file have been created.

 ".mysql_error()."

";    }        if(isset($_post['author']) &&       isset($_post['title']) &&       isset($_post['category']) &&       isset($_post['year']) &&       isset($_post['isbn']))        {            $author = get_post('author');            $title = get_post('title');            $category = get_post('category');            $year = get_post('year');            $isbn = get_post('isbn');                          $query = "INSERT INTO classics VALUES".              "('$author','$title','$category','$year','$isbn')";                            if(!mysql_query($query, $db_server))            {                echo "INSERT failed: $query
".mysql_error()."

";            }        }        echo <<<_END                _END;        $query = "SELECT * FROM classics";    $result = mysql_query($query);        if(!$result) die("Datebase access failed: ".mysql_error);        $rows = mysql_num_rows($result);        for($j = 0; $j<$rows; ++$j)    {        $row = mysql_fetch_row($result);            echo <<<_END        
               Author $row[0]                Title $row[1]             category $row[2]                 year $row[3]                 ISBN $row[4]        
                    _END;    }        mysql_close($db_server);        function get_post($var)    {            return mysql_real_escape_string($_POST[$var]);    }?>

The page is displayed normally, but an Object Not Found Error occurs when you press add recode, and Error 404 is displayed below.
Please help me...

Reply to discussion (solution)

Add a breakpoint for one-step debugging.

Sqltext. php ?? File ??

Does sqltext. php exist?