If you do not want the CustID to be filled from csv file then you can make that field as an identity field and use the following query.
INSERT INTO dbo.Customer
(lastName,firstName,title,address1,address2,address3,postCode,email,fax)
SELECT SURNAME,FORENAMES,TITLE,ADD1,ADD2,ADD3,POSTCODE,EMAIL,FAX
FROM dbo.[NCCUST CSV FORMAT PFS 9.1.14];
Or else you need to delete the primary key, before deleting the primary key constraint, you have to take out the referential integrity constraint and then drop the primary constraint.