[AccessD] setting referential integrity on a 1-1 relation

Dear list,
I have troubles setting referential integrity between two tables, tProject
and tForsys

The first is tProject(proj_id, …) that stores data on projects

The second is tForsys(proj_id, …) that stores other data on projects

Both tables store data of the same entity: a project.

Proj_id is the pkey of both tables.

I settled a 1 to 1 relation between both tables, on the pkey fields, and
need to activate referential integrity. But I get an error message saying
that project has data not ok for the link.

I check with a query that all tForsys.proj_id values are in the
tProject.proj_id set of values.

Obviously, not all the tProject.proj_id values are in the tForsys.proj_id
set of values as tProject is the main table. All projects are registered
within tProject, but not all project s have a correspondant record
within  tForsys
!

Do you have any trick on how to settle referential integrity in this case?

TIA,

Philippe