word文件页面设置提示：运行时错误'91':对象变量或with块变量未设置

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在word中用宏进行页面设置时，如下一段代码，运行时错误'91':对象变量或with块变量未设置。请高手指教
Sub 页面设置()
    Application.ScreenUpdating = False
    With ActiveDocument.PageSetup
        .LineNumbering.Active = False
        .Orientation = wdOrientPortrait
        .TopMargin = CentimetersToPoints(2)
        .BottomMargin = CentimetersToPoints(2)
        .LeftMargin = CentimetersToPoints(2)
        .RightMargin = CentimetersToPoints(2)
        .Gutter = CentimetersToPoints(0)
        .HeaderDistance = CentimetersToPoints(1.5)
        .FooterDistance = CentimetersToPoints(1.5)
        .PageWidth = CentimetersToPoints(21)
        .PageHeight = CentimetersToPoints(29.7)
        .FirstPageTray = wdPrinterDefaultBin
        .OtherPagesTray = wdPrinterDefaultBin
        .OddAndEvenPagesHeaderFooter = False
        .DifferentFirstPageHeaderFooter = False
        .VerticalAlignment = wdAlignVerticalTop
        .SuppressEndnotes = False
        .MirrorMargins = False
        .TwoPagesOnOne = False
        .BookFoldPrinting = False
        .BookFoldRevPrinting = False
        .BookFoldPrintingSheets = 1
        .GutterPos = wdGutterPosLeft
        .LayoutMode = wdLayoutModeDefault
    End With
    Dim ym As String, yj As String
    'ym = InputBox("请输入页眉：", "页眉设置", "", 10, 20)
    'yj = InputBox("请输入页脚：", "页脚设置", "", 10, 20)
    If ActiveWindow.View.SplitSpecial <> wdPaneNone Then
        ActiveWindow.Panes(2).Close
    End If
    If ActiveWindow.ActivePane.View.Type = wdNormalView Or ActiveWindow. _
        ActivePane.View.Type = wdOutlineView Then
        ActiveWindow.ActivePane.View.Type = wdPrintView
    End If
    ActiveWindow.ActivePane.View.SeekView = wdSeekCurrentPageHeader
    Selection.WholeStory
    Selection.Delete
    If ym <> "" Then
        Selection.TypeText Text:=ym
        Selection.ParagraphFormat.Alignment = wdAlignParagraphJustify
        Selection.WholeStory
        Selection.Font.Size = 9
        Selection.Font.Name = "宋体"
    End If
    If Selection.HeaderFooter.IsHeader = True Then
        ActiveWindow.ActivePane.View.SeekView = wdSeekCurrentPageFooter
    Else
        ActiveWindow.ActivePane.View.SeekView = wdSeekCurrentPageHeader
    End If
    Selection.WholeStory
    Selection.Delete
    If yj = "" Then Selection.TypeText Text:=" 第 " Else Selection.TypeText Text:=yj & "   第 "
    Selection.Fields.Add Range:=Selection.Range, Type:=wdFieldPage
    Selection.TypeText Text:=" 页"
    Selection.ParagraphFormat.Alignment = wdAlignParagraphCenter
    Selection.WholeStory
    Selection.Font.NameFarEast = "楷体_GB2312"
    Selection.Font.NameAscii = "Times New Roman"
    Selection.Font.Size = 9
    ActiveWindow.ActivePane.View.SeekView = wdSeekMainDocument
End Sub