I cannot Remotly disarm the alarm and the immobiliser?

The car is a mercedes c200 1996.
The remote transmitter has new batteries and is working
as per the checks in the users handbook(i.e depress the button
for approx 1 sec and the red light in the transmitter should glow !). There is no problem with the car battery and the
inginition turns the engine when I tested it.
The red LED in the mirror flashes ok (once every 20 secs)
The only other thing that might have a bearing , is that it
was raining that day, but I have tested all electrics and they
are working ok.
Donny, October 2007
Danny,
How did you fix this?. I have a similar prob with my 1996 c200 in that alarm and immobiliser are on and unable to use the remote (I also changed batteries)

Mike, November 2007
link Click here to see other fixes for Mercedes.