Mary Rather

I am trying to do the blanket fade tutorial on a newborn photo. I am almost through the layers and mask class and on the list for raw. I follow the steps but when I go to use the brush tool to clean up the edges it says, "the fill layer must be rasterized before proceeding. It will no longer be editable as a fill" and it really gives me no choice. Then the brush will not work. I tried to search the site for this with no luck. What am I doing wrong?