This happens on an POL account with more than 8 FFXI characters. For some reason, playonline is limited to 8 FFXI characters per POL Content ID. If you have 9-16 characters linked and your monthly payment gets interrupted (can happen for a number of reasons), you'll see the message you described. It causes the characters 9-16 to become unlinked from your second POL content ID.

To get rid of it, you can switch to the other content ID with the other 9-16 characters linked, OR ....re-link the FFXI characters which became unlinked when the payment process was interrupted.

It's annoying, but an easy fix.