score:1
Generally a message like this would mean that your reservation has been changed in some way, but the ticket does not match the reservation. I'd suggest reading What is a "backup" flight? - it's not directly relevant to you, but explains the difference between a reservation and a ticket.
Your ticket and your reservation are out of sync for some reason. If your flight is not within the next few days you can potentially just wait a day or two, and you may well find that the problem resolves itself - the airlines systems will likely automatically reissue/revalidate the ticket, and everything will be fine.
If that doesn't happen within a few days, or if you are flying in the next few days, then I'd suggest calling the airline and they will reissue the ticket - this should only take a minute or so, and will not have any charge associated with it.
Worst case they will be able to fix this at the airport when you check-in, but it's best not to leave it until then as it can delay check-in, and will almost certainly mean that you can't use things like online check-in.
Upvote:3
Call the airline and ask. Clearly something has happened to your booking. It would be dangerous to just try to check in, or to wait to deal with it at the airport on the day of departure.