I've actually got a bit of testing and modification to go through here...

That WM_ACTIVATEAPP is being listened to by the MDI-parent form of my app.

I really want this WM_MOUSEWHEEL to be caught by whatever childform has focus.

So I'm off to experimenting with having two WINDOWPROC functions in my app - one for the parent-window and another for this child window/mouse wheel stuff.

But thanks again for this - it's really going to make many of my more sophisticated users happy.