I have a fair bit of information to swap between two workbooks.
From a utility workbook "Bk-a.xls", I compiled a macro as follow.
Line numbers are added for reference here.
I would appreciate some advice on

why line 70+80 failed (application or obj defined error)
but line 60 is OK

line 90 must be in the form as line 100;

Is there ways to avoid switching windows repeatedly please?

10 Sub t()
20 Dim frmBK As Workbook
30 Dim toBK As Workbook
40 Set frmBK = Workbooks.Open("Bk-b.xls")
50 Set toBK = Workbooks.Open("Bk-c.xls")

60 frmBK.Sheets(1).Range("B1").Copy toBK.Sheets(1).Range("C2")
70 'frmBK.Sheets(1).Range(Range("B1"), Range("B1").End(xlToRight)).Copy _
80 'toBK.Sheets(1).Range("C2")

90 'Windows(frmBK).Activate
100 Windows("bk-b.xls").Activate
110 Range(Range("B1"), Range("B1").End(xlToRight)).Copy
120 'Windows(toBK).Activate
130 Windows("bk-c.xls").Activate
140 Range("C2").PasteSpecial
150 End Sub

Regards
Have a happy New Year
KC