2004 S80 Intermittent electronic problem

[Carlxm]

I bought a 2004 S80, used, a month ago and it now gives spurious warning messages.
While driving it will give a warning sign like "Left hand passenger door open" , however this condition does not exist. At this time all gauges stop working, and the interior lights come on, A/C stops working - the engine will keep running and vehicle still drives.
This will occur intermittently and show different error messages each time.
Vehicle was taken to dealers and they cleaned up all the "earth" connections but the problem returned a few days after.