Gambit: Valid entity doesn't exist
 

I defined the boundary types that I wanted but the warning error showed:Boundary entity does not contain any valid entity and is not written. These are the faces that I defined as wall in a volume that I created.

If I were to define the faces as a solid continuum will it be the same?

Most of the tutorial that I had come across are those that doesn't have any objects in the volume created. Is there any tutorial which model something similiar to it??