Generally, with two workbooks open, you need to specify which one to do
something with. There are several ways to do so. The following 2
commands
(4 lines in Book1.xls) do the same thing.

Workbooks("Book2.xls").Sheets("Sheet1").Range("A2: B3").Copy _
Destination:=Workbooks("Book1.xls").Sheets("Sheet1 ").Range("A5")
Workbooks("Book2.xls").Sheets("Sheet1").Range("A2: B3").Copy _
Destination:=ThisWorkbook.Sheets("Sheet1").Range(" A5")
Application.CutCopyMode = False

Hth,
Merjet