Land Rover Repair: No crank 2000 Discovery Series II 4.0 V8, discovery series ii, exciter coil

Question
Bought a used 00 Disco. Don't know the history. It goes into immobilised mode shortly after being switched off. My only work around is to insert the key in the door lock and turn to the unlock position which gives me about a 30 second window to put the key in the ignition and start it. This is most inconvenient. OBD II shows code P1668. The key remote is new and not synched. I have switched out both under dash and under hood fuse panels and the problem persists. I have ordered a used BCU off Ebay. Before I switch that, your input would be appreciated. Thanks

Answer
It sounds to me like the vehicle is set in passive arming mode with the key not being in synch with the exciter coil of the ignition.  I suggest you have your key programmed and the exciter coil checked and the passive arming removed from the programming of the alarm system.  At the same time, ensure that the security module is coded with the engine control module.