This issue has been plaguing me for a while. Initially, it used to come on immediately after starting the car but used to go away after the car ran for a while. Then a couple of months back ( I think with the onset of winter ), it started just staying on. I haven't really bothered because I can still make the call and nothing else seems to be affected. Today, I left the car out in the sun for a couple of hours and when I started the car, the warning was no longer there. I have searched the forum and there is talk of the backup battery failing to hold the charge or water ingress through the antenna but there is no one who seems to have encountered what I am seeing i.e. the light going away when the car is warm. Any pointers? Don't want to spend a mini-fortune taking it to the official service partner.

You'd need to check the TCB or ATM module for faults using ISTA+ to get a better idea of what the issue is.