So.. We're on the AA101 flight from lhr to jfk on monday after a rebooking from BA on sunday. Me and my friend have two different bookings. I can use my BA booking no. on AA.com and select a seat. But when i try to do the same with the other booking no it doesn't work.

"We are unable to retrieve your reservation with the information provided. Please verify your information and re-submit. Otherwise, if you need assistance, please contact AA.com Web Services.
Enter a valid six letter record locator."

Any suggestions. The flight is nearly packed in Y but there has opened up a two-seater that i would like to sit in with my friend.