Random "Secure" message on the screen??
 

I've got an newer shape 02 Primera. The word "SECURE" has randomly started appearing on the screen. Sometimes when this happens the battery goes flat. I've taken the car to an auto-electrician who can't find anything wrong, although sometimes when I stop the car and remove the key the radio stays on and can't be turned off unless you restart the engine. I think because these are random it's difficult to diagnose. Any ideas out there..????