I have simple rigged mesh by automatic weight, I can see the weight color, but cannot paint in Weight Paint mode. I switch from Object to Weight Paint mode, and the brush circle do not effect the mesh when LMB pressed. When I hold ctrl+LMB over mesh it samples the weight into my brush weight. I can use only the Gradient tool for painting. It seems that I'm missing something basic here, but i spent entire day looking for answers and tutorials and can't get it work. Thanks for your answer.