Power Locks - 2004 Ford Freestar

My 2004 Ford Freestar with 130,000 miles just started having a strange intermittent problem. Using the door remote, it will always unlock the driver door but will only intermittently unlock the other doors and the liftgate. The same thing happens using the switches on either front door. The doors will open from the inside using the handles but the biggest problem is that when it happens, you can not open the liftgate at all as there is no interior handle. Any clues?