重复键错误返回

I am working with mysqli database and have email set as a primary key. Now when I attempting to execute() a query on the database, on duplicate entries the database will reject it but I don't get an error returned back. mysqli->errno = 0 however mysqli->affected_rows = -1. How do I get the error that is being returned by the database?

INSERT INTO user (Status,Email,Lastname,Firstname,Password) VALUES (?,?,?,?,?)ON DUPLICATE KEY UPDATE Status = VALUES(Status),Email = VALUES(Email),Lastname = VALUES(Lastname),Firstname = VALUES(Firstname),Password = VALUES(Password)