I've experienced this issue before. A few things come to mind. First the child safety lock is in the on position so the only way (normal door latch operation) to open the door is from the exterior door handle. Second, the latch has disconnected from the rods or the latch has failed entirely.
If you can remove the rear seat cushion bottom sometimes this helps to remove the interior door panel to gain access to the latch mechanism to pull or push the rods connected to the interior or exterior door levers to help open the door.
Also, you could find out way the exterior door handle is not working at this point.
Let me know what you find or have any more questions.
Monday, January 13th, 2014 AT 9:16 PM