Tried to call you but no answer so:
Read the entire Anti-theft section of the service manual and perform all the tests shown. If your mechanic has a Nissan Consult then it will be faster, If not a Volt OHM Meter will do.
If you do that and it passes then look into the BCM*. Do you have any other problems with the car?
*Body Control Module
http://picasaweb.google.com/lh...tlink http://picasaweb.google.com/lh...tlink
The first picture shown above is from the service manual and the second one is from Nissan FAST (A dealer parts program).
If the other stuff also checks out good I would check the shift lock solenoid as shown above.