Intermittent and lots of possible causes... Has this happened when the immobiliser hasn't been set recently? And is that the factory immobiliser... two buttons and a battery in the fob? Any recent work? I'd start (!) by: 1 Measuring the battery voltage at rest, minimum during cranking, and idle. 2 Checking all of the relevant wires: battery, starter, ECU, ignition switch, starter button and relevant earths. Inspect, wiggle, disconnect, clean, reconnect. 3 Having a look at that starter button. Is it really a button rather than a position of the ignition switch? When was it fitted? Would you like a copy of the appropriate wiring diagram? Jonathan