Lightmapping query

Hi - I'm slightly new to lightmapping and have the following problem. I'm baking the lightmaps for a building and when the ground floor is the only active object the scene bakes fine.

But If I have any other object in the scene active (in this case the street) the bake messes up big time. See image.

What can I do to alleviate this ? I've tried changing the lightmap resolution & max lightmap size and I still get the same errors.

Any help would be appreciated in extremis !

 

Hi. Do you have the Generate Lightmaping UVs toggle enabled in the model import settings?

 

yup. On all of the models in the scene.