all lights flashing on my remote control keypad?

I have a challenger home alarm system which is about 20 years old. I needed to replace the remote keypad and was supplied with a challenger AP11RKP. This was quite straightforward, connected the 12v supply then the tamper wires but the other two wires were lettered A and B but the corresponding ones on the main control panel were C and D. When I powered the system back up all the lights on the RKP are flashing and none of the default codes will be accepted. I am wondering if firstly, this RKP is compatible with my system and if so how to fix the problem?