Infinity transponder problem

I just did a 03' Infinity g35 sedan with viper 791xv. I used 556u for the transponder by-pass.  and had the RS set to voltage sense and everything worked fine for about a week then the car came back. The customer was saying that the car cranks but dosn"t start . So I tried to dianosis the problem for four hours still with no luck. I figured it was a transponder problem i had replaced the 556u and still no luck. By this time the customer had to go and he came back the next day to fix the problem. I thought that it was a transponder problem so i played around with ring placement for anothor few hours now i have practially pulled out all of my hair,I confirmed it was a transponder problem by hitting the RS n at the same time as it starts i turn the key n then back off. The RS then stayed on so i knew eveything was alright n it was a transponder problem.  I finallly almost gave up when i took the key out of the 556u then tried to start it to clear the extra gas in the car from the repeated non starts . To my suprise the key dosnt start the car anymore. First thought o....... S#$ts  the car is in protection then i grab the other key n it started the car. It was the most beatiful sound, it started. Now everything works fine. MY problem is In my five yrs of experience i have never seen a dealer key loose memory the key orginally  started the car. I always make sure the key starts the car before i put it in the box.This was one of my worst days  installing. Has this every happened to anyone before and most of all how does it happen? thanks

Image6902 everything worked out fine the orginal key that was in the box didnt even start the car anymore. Don't know how that happened but it did. The other master key when put into the box works fine. You know it was just one of those days. The customer is understanding n told me he had a valet key that he can bring me. I was just wondering how a manafacture key stops working. Those keys are suppose to work the life of the car. I just want to hear everyones experience if any on this so if its something like sticking the key next to a sub or something that erases a key I would like to know. Thanks for your input.