It may be the reed switch on the salt container which is faulty,check salt cap is tight.
use m/c for 6-7 times and check the salt level,if it's gone down it is still using salt and is just the indicator which is faulty so you could live with that by topping up your salt every couple of weeks.
It could be an exspensive repair as it possibly comes as a complete unit with the water softener.
BG, October 2007