Trees that turn black when building the lighting

I have been having this issue where I import a tree into unreal engine 4.10 and everything is there and its working perfectly. When I build the lighting it turns some of the meshes 100% black. I go into unlit mode and the diffuse shows perfectly. not sure if this is a light bug but I cant seem to fix it.

Also I am having a problem with the material painting in landscapes. for some reason when I start painting in this one spot of the landscape it stops showing up anymore. suggestions?

the black issue seems to be something about your UV channel, try to import again your mesh to generate a new UVchannel, it might solve that problem.