Only "Automation" mails receives a barcode. If your mail is "Automation" do you have barcode in your label template? If you have barcode in your template do you have a delivery point field formatted. If you have a delivery point field formatted does it have data in it. If it does not, you must make sure that the length is set to 3 and run address check.

Having either the ZIP Code, ZIP+4 or DPBC field defined a numeric will cause problems with the barcode. If any of these fields are numeric, change them to character under "DATABASE, MODIFY". Then rerun address check to correct the data.