You want to set a field as validated, constrained by a Picklist.
The picklist is not available from the Pick List Name field.
Field Name: DirectorName
Pick List: "DisplayName of Employee"
The DirectorName field is of type "Text".
The Pick List returns the Display Name from Employee.
The Display Name field is of type "Unicode Text".
The types must match for the Pick List to be used.
Changed the DirectorName field to be Unicode Text and the Pick List could be selected.