As said. Before make sure your rods are attached , lubed and free working , on that's stuck will jam up the works also, here's some pics I had of the latch..
I don't guarantee the content of this message it's what the voices in my head told me to type
How the lock and handle rods layot
How the cams are supposed to be lined up when latch is locked:
Allen bolt that's adjusted by the hole in the door above the latch, loose it and move the linkage so the cams line up when in the locked position.