sometimes sensors have a override on them, try switching the power off to the sensor for 30 sec then turn back on, this will reset the sensor. make sure that if you are switching it off with the fuse that when you put the fuse back in you turn the main switch off first.
The general way to turn the sensor onto override is to switch off then on within 3 sec, you want to avoid accidentally doing this with the fuse.
If the light stays on after you have done this then replace the sensor.