Polycom ip560

Hello Everone! I am new in polycom and asterisk world. I have asteisk BE 2.2 and polycom ip560 PHONES. i set the to recieve MWI (Message Wating Indecator) they are working fine; but the issue i am facing is that although i dont have the messages on anyof my polycome phones the MWI beep is light is still on and it is annoying.
Can anyone help me how to resolve this issue.
i can be reached at : mk07md@yahoo.com
Thanks