immobiliser problem?

Hello, my almera 03 plate 1.5cc has aquired an intermitten fault on starting. I unlock as normal but once key is turned all the lights come on as per but no ignition. I have done a diagnostic on ecu and it says a fault on "nats" has been found. Can i reset this or do I need to take it to a Nissan dealership. Any help would be greatly appreciated. Paul