Does it wiggle in an out a little, or just doesn't move at all? If it doesn't move at all, try pushing in and moving a handle to the open position at the same time. As suggested, it may be necessary to push in and up at the same time as well.

The door latch (the part that is on the body) may have moved and needs re-adjusting, which sounds simple, but can be a real pain to get it right.

If it wiggles, the body latch may be real loose and is moving with the door latch and won't dis-engage. If that is the case, you need to get something inside the post to momentarily hold the body latch stationary. Good luck with this, it can be some frustrating trouble.