Redundant - flagged for removal please
when you compare your selector shown by Selector Editor with the one shown in UiExplorer (after you apply e.g. ‘Select Target Element’ to that button), do you see any differences? It is worth to double-check your selectors too in there, e.g. with ‘Validate Selector’ or ‘Highlight’ in Visual Tree tab.
A possible cause of what you’re seeing could be the scope you’re running the activity in. It seems that you’re attached to the Browser, and then trying to click a button in a pop-up window. I have sometimes seen that this can cause problems because some pop-ups are technically not part of the browser window. So, when it looks for the button in the pop-up as part of the browser window, the robot is unable to find it. I’d consider trying this click outside of the “Attach Browser” scope, as this may remedy your issue.