I have exactly the same problem. The instruction leaflet and online pdf do not provide any answers.
The phone is also of questionable quality with a nasty background buzz that wasnt there on the previous one that worked fine for 5 years until the keypad gave up. Also poor sound quality.
All in all a bit of a dog I'm afraid and the damn light is still flashing.
Next time I must remember not to buy a BT handset
Paul M
September 2009