As it doesn't refer to anything like it in the user manual [incedently if you go on to www.bt.co.uk/userguides you can get a download of your manual incase you mislay the one you've got] It's probably some thing simple. I would say unplug the power/charger packe from the base unit and remove the batteries and leave them out for 1/2 hr and see if it resets itself but I don't know if you would lose your listings.
Other than that I can only suggest contacting the BT helpline on 0845 602 1041.
bob
February 2005