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 :huh:-
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  :o 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.

I chose the red box capture mode, objects and regions. I clicked apply and closed the dialogue.
Then I pressed Shift PrSc while the mouse cursor was in my laptop screen. A red box appeared briefly on the laptop screen then disappeared and I couldn't see how to make a screen capture. I moved the mouse cursor onto the second monitor but nothing appeared there either. When this situation occurs if I right click over the screenshot captor icon in the system tray (icon showed a red screen) I have one menu option "Cancel Operation (screenshot Captor)" but clicking this does nothing. I have to use task manager to close Screenshot Captor.
I have now set red box mode to "use never" so at least I can capture on one screen.

I use Teamviewer so if that is an option for you I am happy for you to investigate this yourself if it would be any help.

The problem with screencaptor using a second monitor continues.
The problems seems fairly serious to me.
If I have the mouse cursor on my laptop screen and press Shift PrtSc then for a brief time I see the cross hairs and little grid panel of pixels on the laptop screen and then it disappears although the cross hairs show on the second monitor.
The second monitor is showing a screen capture of the whole screen for me to select an area, but on the laptop screen I can now move the cursor onto it and it is showing applications which I can interact with, and if I put the mouse cursor back onto the second monitor it is still just a screen shot. But now, pressing Esc doesn't get me out of the situation but clicking twice ends the screen capture with an error message because there is no region to copy.
Can anyone suggest what information I can give or tests I can make to be able to provide information on how to fix this problem or to enable someone to provide a fix?
Or, looking at it another way, do people normally find that using a second monitor does not cause a problem?