PHP Problem in uploading

Hi,
I am uploading a file,but it does not work well.
Actually i am using smarty templates and uber uploader progress bar but it does not works. some times file uploaded then that time progress bar does not show any progress.
Any one help me?

//Sample code

$temp="upload";
if(!file_exists($temp)) //if directory does not exist
{
mkdir($temp,0777); //make a directory TMP.
}

$fn=$HTTP_POST_FILES['Upload']['name']; //File name which should be uploaded..
$t=$HTTP_POST_FILES['Upload']['type'];
$s=$HTTP_POST_FILES['Upload']['size'];
$pass = generateRandName();
$newName=$pass . "_" . $fn;
rename($fn,$newName);

$upload=move_uploaded_file($HTTP_POST_FILES['Upload']['tmp_name'], "$temp/$newName");