my wife had the same problem with her Nisssan Almera but this procedure fixed it, so its worth a try........Turn Ignition on till airbag warning lamp goes out (approx 7 seconds) Immediately after airbag warning lamp goes out, turn ignition off for 3 seconds ie 0-1-2-3 or 1-2-3-4 (either way its 3 seconds) then turn ignition back on, Do this this 3 times, after carrying out the above, turn the ignition on for 1 second and immediately turn ignition off, then back on again and start car, this resets the airbag memory. Make sure the under seat connectors are ok.
Hope this helps.