PHP按钮返回404异常

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

_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

<br />               Author $row[0]<br />                Title $row[1]<br />             category $row[2]<br />                 year $row[3]<br />                 ISBN $row[4]<br />        

_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。。。
------解决思路----------------------
加断点一步一步调试。
------解决思路----------------------

sqltext.php 這個文件有嗎？


------解决思路----------------------
sqltext.php 存在吗？