Range "A2:D" is not a valid range reference.

Try something like this...
    Dim vListItems As Variant
    
    ' turn screen updating off,
    ' prevent the user from seeing the source workbook being opened
    Application.ScreenUpdating = False
    ' open the source workbook as ReadOnly
    With Workbooks.Open("C:\ICO\ICO_Import_template.xls", False, True)
        With .Worksheets(1)
            'Range A2 to last used row in column D
            vListItems = .Range("A2", .Range("D" & Rows.Count).End(xlUp)).Value
        End With
        .Close False ' close the source workbook without saving changes
    End With
    
    With Me.ListBox2
        .Clear ' remove existing entries from the listbox
        .ColumnCount = 4
        .ColumnWidths = "50;60;50;40"  'adjust to suit
        .List = vListItems
        .ListIndex = -1 ' no items selected, set to 0 to select the first item
    End With
    Application.ScreenUpdating = True