I don't know if the RR works in the same way as the D2 but I have just had the same problem. I got into the vehicle using the EKA code - first time I've needed it in 17 years, 11 months and 20 days!!! Working as given in the handbook, I got the engine started too, but, next day the same. So, booked it into the garage for two days later and ... guess what - yes - it worked perfectly. It is now with my mechanic to see if he can work out why this happened and to fix it!
Ignore this if it is irrelevant to a RR. But I enjoyed telling you so that you are not alone in your troubles.