The only thing I see "wrong" is that the Dim statement should be:

Dim SixthBook as Worksheet

The way that the code is written, all of the workbooks need to be ope
when you start, right?

If all of the books are open when you start, then you might not want
For ... Next loop. Maybe you want to use For Each.

For Each Window In Application.Windows
Window.Activate
Next Windo

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