check whether you selected the drawing object
Flash has 8 default brush sizes. You can change the brush size by selecting the brush size button in the tool panel while the brush tool is selected. The brush size button is located toward the bottom of the panel if your workspace is set to Essential.
As for the fill and stroke properties menu being grayed out, I am not sure what you mean. Can you please explain further or take a screenshot?
Flash Authoring, QA
Are you using the Brush tool, or the Paint brush tool? While using the Paint brush tool this menu is no longer greyed out and you can manipulate the properties