I've updated the driver and no difference.
But in any case, if I disconnect the second monitor ScreenShot Captor works on my laptop screen as expected, including the red box mode. it's only when I've got the second monitor that it will only work on the second monitor or not at all in Red Box mode.
Here is a strange thing
I changed the layout of my monitors so the second screen is on the right then screenshot captor worked correctly across both screens if I do not have red box mode.
If I use Red Box mode then it worked only my laptop screen and I could drag the red box around the screen. If I dragged onto the second monitor the mouse cursor moved but the red box disappeared and if I move the cursor back to my laptop monitor the red box is there again.
I put the monitor layout back to having the second monitor on the left and now non red box mode works on both screens
but red box mode still only works on the laptop screen.
At the moment I'm quite happy that I can now capture anywhere on 2 screens and I have no idea what has made it work apart from changing screen layouts.