Unable to select seats on Delhi - EWR Air India flight.

I am able to see the seat map and vacant seats available to be picked online on their website, but it keeps erroring out with some weird message "Field flightSegments.recordLocator is mandatory."

I called their 800 number and the agent also could see the seats available that I was seeing online but could not assign them. He then made up an excuse and said I would be able to do it at the time of check in at the AI counter, which is not very helpful :-)

Any advise?