Esta solución no es netamente con CI sin embargo funciona perfectamente:
foreach ($_FILES['field']['name'] as $i => $name) {
if ($_FILES['field']['error'][$i] == 4) {
continue; }
if ($_FILES['field']['error'][$i] == 0) {
if ($_FILES['field']['size'][$i] > 99439443) {
$message[] = "$name excede del limite.";
continue; }
echo $name;
echo '<br />';
$uploads_dir = $config['upload_path'] = './uploads/thumbs/'.$this->session->userdata('raw_name');
$tmp_name = $_FILES["field"]["tmp_name"][$i];
$name = $_FILES["field"]["name"][$i];
move_uploaded_file($tmp_name, "$uploads_dir/$name"); } }