Originally Posted by JJeffrey

I assume this is an award ticket you're searching for...

Unless the JFK-LHR segment is available as sAAver space then you're not going to be able to combine it with the BA segment on the same PNR. This is also why it's not showing up when you search just JFK-CDG.

When using multi-city aa.com will price it out ok initially however it will always error out when you click through as you cannot combine a web-special award with a partner/sAAver award on the same PNR.

And once you start clicking through on a potential booking aa.com will frequently create a PNR of the flights you're trying to book, before you actually book it. This is especially true on itineraries involving partner flights IME. The PNR will sometimes show up in your trips for a short amount of time before it cancels out. This doesn't mean that anything was actually booked though.