Lightmap problem on a Prop

[NightStorm1000]

Hello.

I got a little Problem with my Mesh I made. I got it into Unreal with no Problems but after Lightmap Building I got Ugly Black Corners on my Mesh. Increasing the Lightmap Size works but a 512 Lightmap for a Single Prop is a Overkill.
Is it Possible to use Multiple UV Channels for Lightmap? This would help to Lightmap the Tiny UVs Better.

Screencap of the Lightmapped Prop:

Screencap of the LightMap UV:
https://dl.dropboxusercontent/u/37291956/LightMap%20UV.JPG

I already use multiple UV Channels for Texturing.

[anonymous_user_923c79df]

Have you also added a lightmass importance volume?

[NightStorm1000]

yes. a lightmass Importance Volume is in the scene.

[NightStorm1000]

Fixed it.
Turned on Recompute Normals and Use Full Precision UVs under Build Settings in the Mesh Options and then Used the “Generate Unique UVs” to Regenerate my UV Layouts from Channel 0 to Channel 0.

After that the Corners are gone. Even on Lightmap Resolution 64.
And after the Regeneration of the UVs you can simply turn of Recompute Normals and Use Full Precision UVs.