You have to look and see what causes FT (failure timer) to pull in. When you pull in the CS relay to open the doors, something happened that didn't allow the doors to open, (no UC problem at lobby) and therefore FT timed in and that takes the car out of service. You were saying CST and that sounds like the circuit we used to get out of a CS lockup. CS lockup usually occurred when approaching a floor, not at the floor. But a FT can only happen at the floor. Sounds like there is also a zoning problem, since FT coming in should allow the next zone car to respond.