I have no problem when using BA award tix on CX to check-in online, but I cannot do it if AA issued the ticket on CX. I called CX and asked why could not checkin on web site.. CX rep told that AA uses different system than CX, so CX system was not able to validate the ETKT. BA is using the same system as CX, so CX was able to retrieve ETKT info during the online check-in process.