Transparency Issue

Hey all,

Ok this is my first post and admittedly I am a total noob in just about every respect :)

I have just bought T3D and jumped straight into making my game...

First thing I did was throw in a scattersky, a water plain and some terrain.

I put a tree in (one of the oak trees supplied with the game) and whenever the tree has the sky as the background, the tree appears black...

I have attached a screenshot to try and explain better.

You will see that the tree looks fine when viewed in front of the terrain, but as soon as it sits in front of the sky it goes completely black?

Any help would be much appreciated :)

http://i46.tinypic.com/30ttoya.jpg