Security Code loss

Hi Guy's
Crusty Phil here, I have a 2005 N16 silver 5 speed manual Pulsar. This vehicle has approx 50,000km on the clock and unfortunately has developed a problem of loosing its security code when the engine is turned off and you cannot restart it unless you use the diagnostic tool to reset the code again.
Has anyone else out there in the pulsar community had this problem? I have had the car at Nissan for over 2 months now and they are saying they don't know how to fix it and is very disappointing to say the least. Is there any way I can bridge this **** out so I can start the car? Or is there someone out there that has an N16 computer for sale.

Cheers

Crusty Phil.