When applying case statement with group by and aggregate function it is showing error.

Summary

When applying case statement with group by and aggregate function it is showing error(No fact table exists).I am using 2 subject areas and included fact columns from both the subject areas.

Code Snippet

(CASE WHEN COUNT ("Workforce Management - Person Real Time"."Person Citizenship"."Nationality" BY "Workforce Management - Person Real Time"."Worker"."Person Number") >1  THEN 'Multiple Values' ELSE "Workforce Management - Person Real Time"."Person Citizenship"."Nationality"  END)