It won't let me use brushes...

...okay, I have my sizing problem fixed (thanks again to those who helped!) only to come into contact with another problem. I have a picture sized and I want to use a certain brush to make an outline of a couple things in the picture. Every time I try to use a brush, however, a message pops up. It says: "Could not use the art history because the current canvas size does not match that of the history state."

Can anyone tell me what this means and how to fix it so that I'm able to use the brushes? I would be ever so grateful!

Are you specifically trying to use the art history brush? If so, you'll have to reset your history state with your image sized the way it is now.

If all you want to do is paint with a color on top of what you have, make sure you are selecting the regular brush and not the art history brush.