php 文件下载下来后文件打不开？解决思路

php 文件下载下来后文件打不开？
文件上传代码:
  $page_title='上传文件';
  include('include/header.inc');
  $counter=3; //Number files of allow upload.
  if(isset($_POST['submitted'])){ //hidden form
  require_once ('/conn.php'); // Connect to the database.
for($i=0;$i $filename='upload'.$i; //
$description='description'.$i;
//check for file.
if(isset($_FILES[$filename])&&($_FILES[$filename]['error'] !=4)){
//check discription
if(!empty($_POST[$description])){
$d=trim($_POST[$description]);
}else{
$d=NULL;
}
//添加一条记录到数据库
$query="INSERT INTO uploads (file_name,file_size,file_type,description) VALUES ('{$_FILES[$filename]['name']}','{$_FILES[$filename]['size']}',
'{$_FILES[$filename]['type']}','$d') ";
$result=@mysql_query($query);
if($result){
$upload_id=mysql_insert_id();
// 将上传的文件移动到新位置
if(move_uploaded_file($_FILES[$filename]['tmp_name'],"uploads/$upload_id")){
echo '有'.($i+1).'条文件已经上传';
}else{
echo '有'.($i+1).'条文件上传失败';
$query="DELETE FROM uploads WHERE upload_id=$upload_id";
$result=@mysql_query($query);
}
 
}else{ //if query no ok.
echo '提交有错误请重新再试';
}
}
}
  }

?>

include('include/footer.inc');
?>

文件下载代码：

// Check for an upload_id.
if (isset($_GET['uid'])) {
$uid = (int) $_GET['uid'];
} else { // Big problem!
$uid = 0;
}

if ($uid > 0) { // Do not proceed!

 require_once ('./conn.php'); // Connect to the database.

// Get the information for this file.
$query = "SELECT file_name, file_type, file_size FROM uploads WHERE upload_id=$uid";
$result = mysql_query ($query);
list ($fn, $ft, $fs) = mysql_fetch_array ($result);

  $the_file = 'uploads/' . $uid;

}
// Check if it exists.
if (file_exists ($the_file)) { 

// Send the file.
header ("Content-Type: $ft");
header ("Content-disposition: attachment; filename=\"$fn\"");
header ("Content-Length: $fs");
readfile ($the_file);

} else { // File doesn't exist.
$page_title = 'File Download';
include ('./include/header.inc');
echo '

The file could not be located on the server. We apologize for any inconvenience.

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'; 
include ('./include/footer.inc');
}

} else { // No valid upload ID.
$page_title = 'File Download';
include ('./include/header.inc');