Hello, I am using "data import wizard" to import data in three custom objects named; candidates, positions and job applications. Job applications object has the master-detail relationships with "candidates" and "positions" objects. I am able to import candidate and positions data successfully thru CSV files but when I am trying to import data from job applications CSV, I am getting the error which is (INVALID_FIELD:Foreign key external ID: george@schnell.com not found for field First_Name__c in entity Candidate__c:--).

Candidate object has an email data type custom field which is enabled to get external data in the design but still I am getting above error. Job application CSV has three columns; namely "Email", "Position Title" and "Status". 

Can someone help?