move_uploaded_file returns false

Hello,
Please help in the following problem:
I have written a PHP5 script uploading file:
>
if ($_SERVER['REQUEST_METHOD'] == 'POST' &&
isset($_POST['EditionFile']) && isset($_POST['Year']) &&
isset($_POST['Month']))
{
if (is_uploaded_file($_FILES['SelectEditionFile']['tmp_name']))
{
// Load file:
$file = $_FILES['SelectEditionFile']['name'];
$ext = @substr($file,
@strrpos($file, '.') ? @strrpos($file,
'.') + 1 : @strlen($file),
@strlen($file));
$paper = 'Paper/Blask_' . $_POST['Year'] . '-' .
$_POST['Month'] . '.' .
$ext;
@unlink($paper);
if
(!move_uploaded_file($_FILES['SelectEditionFile']['tmp_name'], $paper))
{
$_SESSION['Error'] = 'Cannot move file.';
}
...
>
The problem is that 'Cannot move file' is reached during execution of the
script. I don't know why. I have checked priviledges on $paper folder:it
looks OK.

What are the priviledges, and what does realpath($paper); tell you about
the directory?