I had this on my 06 plate navara.
I told the nissan dealer it was the solenoid, they said it would just need greasing, so thats what they did..... guess what it didnt work.
I again told them it was the solenoid, they said no, its the BCM unit needs updating, so thats what they did.... guess what it didnt work.
I again told them it was the solenoid, they said no, its the BCM, it needs replacing, so thats was they did..... guess what it didnt work.
I again told them it was the solenoid, they said Yes, its the solenoid, they replaced it and its worked fine ever since. That took 2 or 3 trips to nissan just to solve a simple problem. So from my experience, its the solenoid as mine locked from inside as well but occasionally locked from the key, then stopped totally and i has to manually flick part of the lock with the key or screwdriver and then shut the door. It unlocked fine.