Theres a big old discussion about this on the Octavia forum, and someones just posted showing they've managed to replace the sensor that causes this on a superb.
I had a word with my mechanic about this and apparently it doesn't cause any deeper issues other than the annoying message, as the sensor that
causes it isn't the main one the gearbox uses to identify the gear position, it's more of a secondary back up.
I've decided to just put up with it for the effort and cost involved.
Someone said in the other discussion if you move the gear lever between park and drive a few times before you set off it helps clear the sensor.
I've been doing that for a couple of week now and the warning hasn't come back since, so thats worth a try!