General Sudden System Stops when driving

[Gpang]

I have the 2003 Ulysse (2.0 16V). I've had 2 incidents whereby the engine suddenly stops and I have to shift the key to S and gear to park before I can start back the engine. Initially I thought I had one of the doors improperly closed, but there were no indications of that.
Asked the dealer and they told me to reset the system by turning the key to S for 2 min.
Last night, the alarm went up for a minute before it mysteriously turned off again, by itself.
I need some opinion before I go to the service centres.

Thanks