Dark blocks on some lighmapped surfaces

Hi,
What would cause SOME surfaces on an object to be incorrectly lightmapped? I've attached an image of a "room" where the walls look great apart from a few faces in one corner! I checked the UVs in Blender and all look OK and have tried quite a few things with the lighting settings - but no luck :-(

Looks wrong with Enlighten AND GPU too :-(

Thanks!

 

Are you sure the "Generate Lightmapping UVs" is checked in the import settings of the model?
What do you mean by you checked the UVs in Blender? Are trying to import your own UV2?

 

I was getting some artifacts on objects in the blender scene when using "Generate Lightmapping UVs" so I unchecked it. This meant I had to ensure all objects in the blender scene had "good" UV mapping. Having done that though, I still got those marks on some objects and can't trace why it's happening.