power door lock system will not unlock any of the doors

I saw this and was hoping someone had the answer. I have a very similar problem with my 2008 Chevy Uplander. All the doors lock with the door switch, fob, or putting the van in gear, but only the driver's door with unlock. In my case I have the fob and I tried changing out the battery, but no joy. Everything stays locked except the driver's door unless I manually unlock it at the door (the tailgate staying locked all the time now).