It sounds like an alarm problem keeping the doors double locked, but the starter not engaging does not seem right.
Unless you have different system then mine, when armed the same with the doors but the engine cranks, just no fuel or spark.
It happened 3 days ago in a parking lot, the engine cranked but did not start, turned the key off and on then it started...hummm just a fluke.. SO I THOUGHT untill it happened last night in the rain @ 65 mph EVERYTHING died, when I pulled over the engine just cranked untill I hit the sunroof control panel a few times.
I can't seem to find anything in the Bentley Manual on the system. so am about to pull the panel as I type this..
I'll let you know what I find it is any help to you