Ours has suddenly stopped letting the cats in from the outside, even though we set it with their chips. I can't find the manual anywhere of course!! Ive spoken to the help line but i'm being told to remove the four white buttons to reveal the screws underneath but although there are four white bits on the front they certainly don't look like removable buttons and i can't get the off for love nor money! Does anyone have this same model I wonder? It's about 18 months old.