I was encountering this problem on my meshes until I found the Light Map Coordinate property inside the UE4 static mesh editor. By default after importing it was set to 0 (aimed at my diffuse UV channel) and had to be set to 1 (aimed at my lightmap UV channel). After changing this I no longer got the lighting build error and the shadows are appearing correctly.
In my workflow I use Blender to create my meshes. Each mesh has 2 UV channels, the first for diffuse texture (where overlap is fine) and the second for lightmap (where overlap is a problem). In Blender you can generate your lightmap UVs via LightPack, if you specify a margin of 1.0 then you will definitely not have any overlap. The key part of the Light Map Coordinate setting is to make sure that UE4 is using the correct UV map.