Fixing lighting on billboard terrain trees in Unity Free

Hey guys,

I have tried for days to no avail fixing billboarded trees on the terrain tree editor - i have ensured my shaders are set to Ambient Occlusion Bark and Leaves as well as even putting them inside a folder named Ambient-Occlusion (and reimporting) but i just can't get it to work

To show what I mean i attach a screenshot:

https://dl.dropboxusercontent.com/u/25535993/treebb.png

really ruins my night scenes

I have just about exhausted all the threads and posts I can find relating to this so any assistance would be really great

Thanks all