Faulty lighting on mirrored object

SleepyRosenborg

As the title says, I've run into a pesky thing which I know for certain is due to the object being mirrored, but have no idea how to fix it.

Lighting built:
Lighting unbuilt:

SwdPwnzDggr

What are your UV sets like?

radiancef0rge

looks like your lightmap uvs need work

SleepyRosenborg

The one on the left is the one I use for the texture, UVchannel 0. The one on the right is automatically made by the engine I assume, is this something I should do by hand? and if so how?

SleepyRosenborg

I can add that I unwrapped it in 3ds max, and have never really managed to reliantly create multiple UVchannels, though I have tried and managed to do it by accident.

Obscura

I would never want to rely on automatic unwrapping, especially with lightmapping. You need to be really careful with the seams with them, and hide them as much as possible. There are so much tutorials on the internet for making multiple uv maps with Max.