If you will post what ACR means I will move your message to the applicable program forum where other users may be able to help
Hi John - ACR is for Adobe Camera Raw
I think it means "the sliders are all 0 so painting adjustments with this brush won't change anything." In other words, move one of the sliders to a non-zero position, for example Exposure from 0 to 1.0, and then see what happens. You can edit the brush and change it to do something other than Exposure +1.
Yes, it's one of those messages that is displayed so that you don't have to come to the forums to ask why the adjustment brush isn't doing anything. All that is necessary is to set any one the adjustments to a non-default setting, and that message will not appear.