Go back and edit your W-2; you will need to exit the review section. Are boxes 19 and 20 blank? You can leave boxes 18-20 all blank if there is no tax withheld, but if there is tax withheld in box 19, you will need entries in boxes 18 and 20. To go back to your w-2, search for w-2 and use the jump to link. Then click edit or the pencil icon next to the w-2 that has the error.