I had this happen a few months ago. In my case only one side was stuck, so I was able to reach in the other side. If both are stuck, you will probably have to remove the box (put the top down, twist the two locks and pull it out of the car). I cannot remember exactly what I did, but the accordion door was getting stuck on a small piece of plastic, not a stray piece but part of the actual box/door guide. I pushed on the plastic and wiggled the door and it has worked fine since. I am sure you will be able to figure it out once you get in there.
