Just had this happen to me on an AA-issued (a few weeks ago) eticket. The ticket was reissued a few times before. Tried both checking in by record locator and eticket number. Both got me to the first screen and the same error. Called CX and the first one said something along the lines of "American did update the record correctly, it's out of our control, but you can definitely check in at the airport." The second one didn't actually say American did something wrong, but said something along the lines of: "this is not issued by us, I'm sorry about that but you'll be able to check in at the airport without problem."

Both were able to read off the right eticket number to me.

Of course, this smells like an issue on the CX side. If the right eticket number is in the booking, why are you blaming another carrier for your system's inability to find it?

I went to sleep, woke up the next morning, and OLCI worked. So I guess if you get this error, uh, maybe try again in a few hours?