Can't get Range Mask to turn on
I just installed the latest Lightroom Classic CC version 7.0. I have followed the instructions to use the new Range Mask tools. I created a mask using the graduated filter and selected the Brush option. Range Mask is grayed out and clicking on it has not effect. So, I am not able to use it at all. I tried updating my video driver, but that had no effect. I am using Windows 10 with an Nvidia Quadro M4000 video card. Anyone have any idea why I can't access the Range Mask?

