UV transparency not working

here’s a picture of what i’m talking about

 from the picture, you see that the tree in the center having transparency perfectly fine, but the tree at the left is not,  but some time they would look fine,  why is it that only at certain angles the transparency would work?  :)

Do you have the specular slider turned all the way down to zero for the material in question? Specular highlights are reflected even from zero alpha textures! If this doesn’t solve your problem then you’ll probably need to upload a .blend file so that it can be disected.