It's doing it to me every time in FSX..... ever since that load of Live Update in June.....
As I've said, this is not normal, cannot replicate it, and the only possible reason why it might happen, is there's something wrong in the Compatibility setting of the sim or in your user account that, for some reason, has issues with writing in the registry.
Some very aggressive and bugged antivirus *might* also be the cause of this. Maybe, they are preventing the activation keys to be written in the registry, because the defective antivirus has decided it might be dangerous.