Hi,
When BSP/Geometry are converted to static meshes their UVs are not the best. If you have multiple that you are converting into meshes their UVs will be laid on top of each other. It would be best practice to export he mesh and correct the UVs in an external modeling software like 3Ds Max, Maya, or Blender. You can use the auto-generated UVs in the mesh editor/Viewer but this will likely produce less than desirable results.
To go back to the blackness you’re seeing this is because the UVs are stacked on top of each other. No amount of adjusting the lightmap resolution will fix this.
If you have any other questions please let me know!
Tim