에러좀 찾아주세요

책에 있는 소스를 실행했는데, 에러가 납니다. 어디가 잘못 되었는지요.

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source : php와 html을 사용해서 간단한 인증 구현
===============================

<?php
// 짧은 스타일의 변수로 만든다.
@ $name = $_POST['name'];
@ $password = $_POST['password'];

if(empty($name)||empty($password))
{
//방문자는 이름과 비밀번호를 써야 한다.
?>
<h1>Please Log In</h1>
This page is secret.
<form method="post" action="secret.php">
<table border="1">
<tr>
<th> Username </th>
<td> <input type="text" name="name"> </td>
</tr>
<tr>
<th> Password </th>
<td> <input type="password" name="password"> </td>
</tr>
<tr>
<td colspan="2" align="center">
<input type="submit" value="Log In">
</td>
</tr>
</table>
</form>
<?php
}
else if($name=='user'&&$password=='pass')
{
// 방문자의 이름, 비밀번호쌍이 맞는 정보였을 때.
echo '<h1>Here it is!</h1>';
echo 'I bet you are glad you can see this secret page.';
}
else
{
// 방문자의 이름, 비밀번호쌍이 틀렸을 때.
echo '<h1>Go Away!</h1>';
echo 'You are not authorized to view this resource.';
}
?>


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에러코드
===================

Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, webmaster@localhost and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.


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Apache Server at localhost Port 80