PHP deleting file from another harddrive

I’m trying to delete a file which is on another hard drive (F:)

$filePath = $_POST['path']; //F:/documents/918/20221117.pdf
unlink($filePath);

It just throws

Warning: unlink() [function.unlink]: No error in C:wwwdeleteFile.php on line 351

PHP Version is 5.1 (yup…)