Are your CAB-1 batteries old?
I forget specifically the situation, but I seem to recall some users have reported that some functions of the CAB-1 stop working before other functions do when the batteries start to go. (i.e., it's not "all or nothing" in terms of working)
I don't recall for sure if it's the keypad that stops working first, but it's worth swapping in 4 fresh AA batteries as a quick check to see if that's it.
-Dave