I had the exact same problem a few weeks ago. The pin is most likely out of alignment. First, you have to crawl back into the cargo area, and pull back the carpeting. This will expose the manual release cable. If you're very lucky (I wasn't), pulling on this cable might release the pin. Then, all you have to is very carefully re-align the pin by loosening the two 10 mm nuts underneath the pin assembly.
If this doesn't work, you still need to remove the 10 mm nuts on the bottom of the pin assembly to get the cover pieces off, except you'll have to do it on your belly inside the cargo area with the hatch stuck closed. Hopefully you're a slim guy <img src="/forum/images/smilies/968/biggrin.gif" class="smilie" alt="" /> . Then you just have a lot of struggling and grunting ahead of you as you try to push the pin, which you will now have some access to, up from the bottom. About 30 minutes of struggling, walking away form it several times to clear my head and re-think my strategy, finally did it for me. Hopefully yours will be easier than mine was. Best of luck.