Occlusion System is working now.

It was just down to the initial min/max values for the bounding boxes.

They were originally set to zero.

I just changed them to this:

zone\max_X = -1000000.0
zone\max_Y = -1000000.0
zone\max_Z = -1000000.0
zone\min_X = 1000000.0
zone\min_Y = 1000000.0
zone\min_Z = 1000000.0

They needed to be set to very large numbers - i.e. outside the dimensions of the level map.

Zero coordinates fall inside the level map, so it was getting screwed up.

Regards,

Rogue Vector