'With-in' duplicate GPRBuild name files

Question

I try to build a_project (3rd party) where:

a_project.gpr
--> with config.gpr
--> with a_lib.gpr

a_lib.gpr
--> with config.gpr

note 1: config.gpr in a_lib and a_project are distinct files.
note 2: both config.gpr are 'abstract project'.

The building process tells me:

config.gpr:15:18: duplicate project name "config"
config.gpr:15:18: already in "...\a_lib\config.gpr"

What should be done to make this work?

Thx.