I had the same thing on my car. Pads were replaced before wear sensor triggered. I had to replace the sensor to fix, they seem to be a two stage trigger, even if the final stage is not worn into, the first trigger will mileage count down and not resettable. Once it was replaced, AND DROVE it, it reset itself. Anyway that was my experience.
Cheapest prices at AutohausAZ ($15):
http://www.autohausaz.com/search/pro...0Wear%20Sensor