I like also sun and heaven object from AC9 library.
Please try to do this one:
For outside rendering Cameralight is not so good (without camera light more soft)
Did you have right things in LW options? (Sun out, ambient on, lamps on etc.)
Make heaven intensity higher.
If it ist also too dark, than go to material, and see diffuse and something like that (I don't know, engish word...)
You can there material more brighter.