Door problems of the 2006 Nissan Xterra

Tried to open rear drivers side passenger door, and will not open from outside or inside of vehicle. Checked locks, opened with the key fob and internal unlock button and you can hear it disengage, yet door will not release. This is a the second time we've had this issue with a Nissan Xterra; once before on another Xterra, model year 2006 as well, and now this 2006 that we purchased used 4 years ago. If this were to happen and not know it; and had to vacate the vehicle in a hurry; would present a safety issue in that most times our children are in this rear seat. That it has happened on two separate vehicles we've owned, the prior one it happened within the factory warranty time, and now this one, and upon reading about it online, it is happening to others with this model year. We were told it was the actuator on the other one, but seems to be a part that is an issue, and not necessarily based on the age of the vehicle.