Problems when deleting files with php - php

Question

I've done some code to try delete the cache, and I got it working on my own computer. However, I've ran into a few problems with doing it on my website
The code is here -
<?PHP
function getFiles($dir,$hours){
//read files
$files=glob($dir.'/*');
for($i=0; $i<count($files); $i++){
//get last modified time
$lastchanged = (time()-filemtime($files[$i]))/3600;
echo $files[$i]." modified: ".round($lastchanged)." hours ago<br/>";
//loop into folder if folder
if(is_dir($files[$i]) == true){
$listoffiles = getFiles($files[$i],$hours);
if(strlen($listoffiles)==0){
rmdir($files[$i]);
}
}
//delete file
else{
if($lastchanged > $hours){
unlink($files[$i]);
}
}
}
}
$dir = 'thumbs/cache';
echo getFiles($dir,7*24);
?>
However, on the website, it doesn't seem to detect if the folder only contains another folder, so tries to delete it, and then causes an error saying the directory is empty.
Can anyone see what I've done wrong? Other than this problem it seems to work all right on the site, I did try storing a list of all the folders, reading it backwards, and trying to delete everything backwards so it'd get the empty folders first, but that didn't work either.