I've taken a color picture and made it black and white by doing the following: Layer>New Adjustment Layer>Hue/Saturation. I brought the saturation down to -100. The pencil is selected and my foreground color is black.
When I try to select the flowers in my picture to bring out their color (within the black and white image), I get a circle with a black line thru it and the error message "could not rasterize because the pixel data for this layer is not directly editable". The steps I followed are working for most of my team but some of us are getting this error message.