That error usually means the columns you mapped (Category, Company, Email, External ID, Subsidiary) are empty in at least one row of your CSV. It isn’t a mapping problem. Check for these:

1. Blank cells or trailing empty rows. Filter each of those columns for blanks. Rows left over at the bottom of the file are a common culprit.
2. Unmap fields you don’t need. If you’re importing contacts before their entities, Oracle says to use External ID as the reference type and not import values for the Contacts’ Company field. If some contacts have no company yet, unmap Company. The same goes for Category if it isn’t mandatory in your account.
3. Keep Subsidiary. In OneWorld, Subsidiary is required for contact imports, and the values should be hierarchical names in the format grandparent : parent : child. Since you mapped it by internal ID, confirm every row has a valid ID.

   If it still fails, check the delimiter and encoding in the Import Assistant’s first step. A wrong delimiter shifts columns and makes fields look empty.

— Ankur, Polytope