I got an error message as following while consulting the orders

Notice: Undefined index: booking_upgrades in hotel_booking_order_details_table() (line 144 of mysite.com/sites/all/modules/uc_hotel/hotel_booking/hotel_booking.panes.inc).

I then modified line 144 in the hotel_booking.panes.inc

From : if (count($item->data['booking_upgrades']) == 0) {
To: if (isset($item->data['booking_upgrades']) && (count($item->data['booking_upgrades']) == 0)) {

The above solved my problem. Just take note here in case anyone else got the same error.