The keys are not recognised by the immobiliser, so it thinks you are trying to steal the car. Both keys have transponders in them. The larger key has a fob with the remote locking and alarm transmitter in it, a completely separate item from the immobiliser.
There is no DIY way of recovering from this, if there were it would be used by car thieves. The dealer will have to find out what's wrong (immobiliser reading coil if you're lucky, ECU if not), replace it and reprogram the immobiliser to recognise all of your keys. He will only do that after you have proved to him that it is your car, registration documents and means of identification will probably be called for.