George,
I think that I know this car and if I am correct then I suggested to the owner to remove the Toad alarm system as a process of elimination and the Nissan garage was about to do this when the owner changed his mind and removed the car from the Nissan garage and returned it to yourselves, the supplying dealer.
I know how to remove the Toad alarm system and also how to install the NATS code permanently but in case this is not the same car then I suggest that in the first instance you contact Toad @
http://www.toadalarm.com/?kw=toad%20sec ... 4wodfQvpjw
If I can be of any further assistance to you then you know where to find me.
We really are a friendly and obliging bunch on this forum and I hope that you hang around long enough to find out.