Originally Posted by emcampbe

Even for regular economy, for non-elites, there are free seats (those in white), and paid seats (Economy+, those in blue with extra legroom, and I think you can also buy preferred now, which are the same as the regular white seats, but they are closer to the front - they are half white half dark blue (IIRC), and used to be only available for certain pax - elites, corporates, etc.). When all the free seats are already selected, the message you are getting pops up, because, there are no free seats left to select.

You can keep checking - things do change - people might cancel, buy up, change flights, etc, so free seats could become available again. Failing that, you could elect to pay for one of the paid seats (IIRC, the option to buy to E+, though not sure about preferred, isn't available on a basic ticket). As you get closer to departure, and especially at check in, things can get better. You have elites (silvers) who are eligible to move into E+, others who might buy up, etc. In the absolute worst case, you;'ll be assigned a seat automatically at check in or at the gate, for free, even if the seat was one of the paid options from earlier.