ActiveWindow.Width no longer works for me!
 

Thanks Jim

I saw that info in the help file, but as the Excel window was normal, I
totally missed the fact that the worksheet window within Excel was
maximised.

I made the change, fully expecting the problem to remain - but it went.
That's how the subtlety between the Excel window and the worksheet
window became clear. Ah well, I guess I should trust the Help files
more and try out what they say, even if it doesn't seem relevant!