Association '{0}' on Entity (External Content Type) '{2}' with Namespace '{1}' does not match the foreign key status of other ...

Association '{0}' on Entity (External Content Type) '{2}' with Namespace '{1}' does not match the foreign key status of other Associations in the same direction of AssociationGroup '{3}' on Entity '{5}' with Namespace '{4}'. Associations with the same direction in an AssociationGroup must either all have foreign Identifiers embedded, or they must all not have any foreign Identifiers.