Having spent out quite a bit on mine this year - I feel your pain. This feels like it's final finer to me for 2014!!
If you have got halfway through the programming sequence, you will have effectively 'unlearnt' the existing fobs.
Having done some reading this morning, there appears to be two methods for teaching the codes;
This one...turning the key on and off 6 times at the start
http://www.350z-uk.c...te-not-working/
And this one....taking the key in and out at the start
http://my350z.com/fo...rogramming.html
I haven't tried them yet - but having read as much as I can find on it this morning, it is recognised that it takes a couple of goes (much like the pedal dance) to get it right. There was also someone that commented that when starting the sequence with the 6x on/off that you had to do it reasonably quickly and ensure that you got to the right points of the ignition barrel.
Not saying that you aren't doing it properly - but I would give it a couple more goes before you consider opening the car with a brick for the rest of it's life
If all else fails, you will need to look up a Nissan specialist that has Consult - they will be able to not only recode but also to diagnose if the fob is knackered
Keep us posted!