Undo Brush Tool, History Snapshot

[dlo 2019]

Im new to Affininty, Im trying to use my undo brush tool and when I try it says I must select a history snapshot before trying to undo. I do not know what that means. Ive tried to take a snapshot and that doesn't work. Any help would be greatly appreciated. 

[toltec]

9 hours ago, dlo 2019 said:

Im new to Affininty, Im trying to use my undo brush tool and when I try it says I must select a history snapshot before trying to undo. I do not know what that means. Ive tried to take a snapshot and that doesn't work. Any help would be greatly appreciated. 

If you click on a camera icon, it will go dark (as shown) and your Undo Brush Tool will undo to that  history step.

[Anthony42]

I have exactly this problem; I used the brush ages ago on a different picture, and have not been able to use it since.  It calls itself Undo Brush Tool. I've tried the method advised above; the camera symbol goes white, but nothing happens.  Also tried Control+ Z (as advised in the Edit section).  The Paintbrush button still says Undo Brush Tool. Please help if there's a way out of this! Thank you