Security light on

I own Toyota Camry 2006 GL, here is the description of the problem, car refuse to start, and once I put the key in the switch, the light of the security wont to be off, so the light of the security keep flashing, that is mean the can cannot identify the Key(Both master key and the Spare Key), this problem happened before and I sent to a car technical Electric, and what he is saying he fix some electricity on the car and Re-Program the key, and it work fine, now it is Five months later and yesterday same problem again happened and the car Dose not want to start, the engine is crank but not fire up. And I call one of the guys to Re-Program the keys again, but it is still same problem, car wont to start.

if any of you know the cause of the problem, and how to know which part need to be replace, I want to Limit the scop of the problem.