Hello I'm having trouble with the history brush tool, so it would be great if someone could help me out. Everytime I click the history brush, something pops up and says "could not use the history brush because the current canvas does not match that of the history state". What does that even mean, and how could i fix this problem?

Many thanks

.... I assume you can only use the history brush when your canvas matches the conditions of the previous canvas. So, same size and colours ... Ect.

Why are you using the "history" brush in the first place? Why not just use the brush tool?