As per another thread on here. I have same problem but have not tried it yet. GOOD LUCK and fingers crossed!
"Do you have the remote with two grey buttons or has it got one yellow and one green?
If the first with two grey buttons then this is probably what you need to do.
Assuming the remote appears to work, ie the light comes on.
Press and hold both buttons together, the light will flash as you do this, wait till the light goes off (about 10sec) let go of the buttons and the light will come back on, press the larger of the two buttons, the light will flash then go off, press the same button again and it should arm/disarm.
If its the other type with the green and yellow buttons it may be a build up of carbon on the PCB, open it up and clean where the button makes contact with something that wont damage the circuit, or possibly need reprogramming."