Tilt your camera up about 45degrees - or even 90 degrees. You get nothing but sky. It's a pian to model like this but 
1, you can model your scene
2, select all
3, rotate up to 90degrees (include the camera)

I suggest you make a simple box prim and try it with that first.

or (if you don't know what I'm talking about)......

start Bryce
click and hold the big ball to the left of the work area
drag it upwards
render...........

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All the Woes of a World by Jonathan Icknield aka The Bryster

And in my final hours - I would cling rather to the tattooed hand of kindness - than the unblemished hand of hate...