$ HTTP_POST_FILES无效

It's not showing the details of the files so I'm not sure if they are even uploading or not. Here is the start index.php file with the form:

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Multiple File Upload</title>
</head>
<body>
<form action="multiple_upload_ac.php" method="post" enctype="multipart/form-data" name="form1" id="form1">
  Select file
  <input name="ufile[]" type="file" id="ufile[]" size="50" />
  <br>
  Select file
  <input name="ufile[]" type="file" id="ufile[]" size="50" />
  <br>
  Select file
  <input name="ufile[]" type="file" id="ufile[]" size="50" />
  <br>
  <input type="submit" name="Submit" value="Upload" />
</form>
</body>
</html>

and here is the page it posts to (multiple_upload_ac.php):

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Upload Details</title>
</head>

<body>
<?php       
  echo "File Name :".$HTTP_POST_FILES['ufile']['name'][0]."<BR/>"; 
  echo "File Size :".$HTTP_POST_FILES['ufile']['size'][0]."<BR/>"; 
  echo "File Type :".$HTTP_POST_FILES['ufile']['type'][0]."<BR/>"; 

  echo "File Name :".$HTTP_POST_FILES['ufile']['name'][1]."<BR/>"; 
  echo "File Size :".$HTTP_POST_FILES['ufile']['size'][1]."<BR/>"; 
  echo "File Type :".$HTTP_POST_FILES['ufile']['type'][1]."<BR/>"; 

  echo "File Name :".$HTTP_POST_FILES['ufile']['name'][2]."<BR/>"; 
  echo "File Size :".$HTTP_POST_FILES['ufile']['size'][2]."<BR/>"; 
  echo "File Type :".$HTTP_POST_FILES['ufile']['type'][2]."<BR/>"; 
?>
</body>
</html>

But something is wrong because i'm getting empty output:

File Name : File Size : File Type : File Name : File Size : File Type : File Name : File Size : File Type :

I've tried to keep the code to a minimum while replicating the problem. Any help would be greatly appreciated :)