Hi tjcom,
we have this mistake happen all the time on our system. What happens is a user dials the station number followed by a 6. This sets the message waiting light flashing. Or someone has set a call back message on the phone.
There are two ways I have seen it removed:
To remove the light go to CM 20 and create an access code to = A46 (IVS) or A146 (IVS2). Go to the station with the light, dial the access code from the Prime followed by a 3.
Another way we do it is by picking up the offending phone's reciever, and press my line followed by 613 then hang up. This should clear out the message light.
I hope this helps...