Switching between workbooks

Good evening,

I am trying to import data from one workbook into another but it is not working. Any ideas on what is happening? This is something I am piecing together from other posts but I have hit a snag.

Sub Updating()
Dim ImportFileName as Variant
Dim CFileNeams as Variant

    CFileName = ActiveWorkbook.Name
    MainMenu.Hide

    spath = CurDir
    ChDrive ThisWorkbook.Path
    ChDir ThisWorkbook.Path & "\Import File"

    ImportFileName = Application.GetOpenFilename(filefilter:="Excel Files (*.xls),*.xls", MultiSelect:=False)

    If ImportFileName = False Then
        MsgBox "Error"
        MainMenu.Show
    Else
        Workbooks.Open Filename:=ImportFileName
    End If

ImportFileName = ActiveWorkbook.Name
    Application.WindowState = xlMinimized
    Windows(ImportFileName).Activate
        Sheets("Setup1").Select
        Cells.Copy
    Windows(CFileName).Activate
        Sheets("Setup").Select
        Range("A1").PasteSpecial Paste:=xlPasteValues
        
    Application.WindowState = xlMaximized
End Sub

It works up until Windows(CFileName).activate
I am not sure what is happening here as I have checked, using a message box, and CFileName still has the correct file name. For some reason excel will not switch to the other file. If I switch this to Windows("Workbooks name.xls").activate the code works.

Any ideas? As always, thank you in advance for your help!
tc