PHP按钮返回404错误

书上的内容，然后已经建立了数据库和login.php文件。

<?php    require_once 'login.php';    $db_server = mysql_connect($db_hostname,$db_username,$db_password);    if(!$db_server)die("Unable to connect to MySQL:".mysql_error());    mysql_select_db($db_database)    or die("Unable to select to MySQL:".mysql_error());        if(isset($_post['delete']) && isset($_POST['isbn']))    {        $isbn = get_post('isbn');        $query = "DELETE FROM classics WHERE isbn='$isbn'";                if(!mysql_query($query, $db_server))        echo "DELETE failed: $query<br />".mysql_error()."<br /><br />";    }        if(isset($_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<br />".mysql_error()."<br /><br />";            }        }        echo <<<_END        <form action="sqltext.php" method="post">                    <pre class="brush:php;toolbar:false">                                  Author <input type="text" name="author" />                   Title <input type="text" name="title" />                Category <input type="text" name="category" />                    year <input type="text" name="year" />                    ISBN <input type="text" name="isbn" />                                        <input type="submit" value="ADD RECORD" />                        

_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]); }?>
该网页显示正常，但是一按ADD RECODE按钮就会出现Object Not Found错误，并且底下有Error 404。
求大神帮忙呢。。。

回复讨论(解决方案)

加断点一步一步调试。

sqltext.php ??文件有?？

sqltext.php 存在吗？