Flat Surface Bugged???

Hi, I have a great problem with my WE recently, I can't no more flatten precipices! I mean, I can flatten a surface to make it smooth without imperfections, but I can't no more use the flat tool to flat for example a 2-level precipice to normal terrain level, it simply doesn't work! What is this??? Thanks.

Make sure you use Flattening tool under Cliffs not the ones with Raise/Lower/Smooth/Noise.

Ok, i simply unistalled and reinstalled it. My pc messed something... 10x btw.