Having run a body shop for 8 years, I know a thing or two about airbags. This can be caused by a few different things.. If it was a roll over, the SRS system would've been activated and curtain as well as side airbags should've deployed. It's possible the seat bags were not deployed, but the signal for them to deploy may have burnt out he resistor in the airbag. You may have to bring it in to Ford for them to check it as only the dealer has the propriety software to test each individual airbag to determine if they are functioning properly or not. Did u try to turn off the code with your Accessport? I've never tried so I don't know if it will work or not. Did you disconnect the battery of the car while you swapped seats? Of not, disconnect the battery for 1 hour and then reconnect and start the car to see if it goes away. This is a simple way to reset if you didn't disconnect the battery when you swapped the seats. I would start with disconnecting the battery first and go from there.