pHP文件下载代码，求各位大神给看看那哪里错了

//文件下载函数
//$file_path 文件下载路径
//$file_name 文件名
//$file_sub_dir 下载文件子路径
function down_file($file_name,$file_sub_dir){
//如果文件名字是中文，转码
$file_name=iconv("utf-8", "gb-2312", $file_name);
//绝对路径
$file_path=$_SERVER["DOCUMENT_ROOT"].$file_sub_dir.$file_name;
//打开文件
if(!file_exists($file_path)){
echo "文件不存在！";
return;
}
$fp=fopen($file_path, "r");

//获取文件大小
$file_size=filesize($file_path);

//返回的文件
header("Content-type: application/octet-stream");
//按照字节大小返回
header("Accept-Ranges: bytes");
//返回文件大小
header("Accept-length: $file_size");
//客户端弹出对话框，对应的文件名
header("Content-Disposition: attachment; file_name=".$file_name);

//向客户端回送数据

$buffer=1024;
//为了下载安全，做个文件字节读取技术器
$file_count=0;
//判断文件是否结束
while (!feof($fp) && ($file_size-$file_count>0)){
$file_data=fread($fp, $buffer);
//读取了多少字节
$file_count+=$buffer;
//把部分数据传给浏览器
echo $file_data;

}
//关闭文件
fclose($fp);
}
file_down("1.jpg","/test/");
?>

回复讨论(解决方案)

下面是错误

Warning: fopen(C:/AppServ/www/test/) [function.fopen]: failed to open stream: Permission denied in C:\AppServ\www\test\FileDownServer.php on line 16

Warning: Cannot modify header information - headers already sent by (output started at C:\AppServ\www\test\FileDownServer.php:16) in C:\AppServ\www\test\FileDownServer.php on line 22

Warning: Cannot modify header information - headers already sent by (output started at C:\AppServ\www\test\FileDownServer.php:16) in C:\AppServ\www\test\FileDownServer.php on line 24

Warning: Cannot modify header information - headers already sent by (output started at C:\AppServ\www\test\FileDownServer.php:16) in C:\AppServ\www\test\FileDownServer.php on line 26

Warning: Cannot modify header information - headers already sent by (output started at C:\AppServ\www\test\FileDownServer.php:16) in C:\AppServ\www\test\FileDownServer.php on line 28

Warning: feof(): supplied argument is not a valid stream resource in C:\AppServ\www\test\FileDownServer.php on line 36

Warning: fread(): supplied argument is not a valid stream resource in C:\AppServ\www\test\FileDownServer.php on line 37

Warning: feof(): supplied argument is not a valid stream resource in C:\AppServ\www\test\FileDownServer.php on line 36

Warning: fread(): supplied argument is not a valid stream resource in C:\AppServ\www\test\FileDownServer.php on line 37

Warning: feof(): supplied argument is not a valid stream resource in C:\AppServ\www\test\FileDownServer.php on line 36

Warning: fopen(C:/AppServ/www/test/) [function.fopen]: failed to open stream: Permission denied in C:\AppServ\www\test\FileDownServer.php on line 16
说的很明确了！
Permission denied 中文释义：权限被拒绝