Method intersect of object global failed

[dpaton05]

I have a spreadsheet and I try and run the following code in module 4

Sub LateCancel()

        Dim ws As Worksheet, sh As Worksheet, sht As Worksheet, QT As String, wb2 As Workbook, WbPath As String, QTPath As String
        Set wb2 = ThisWorkbook
        QT = "CSS_quoting_tool_29.5.xlsm"
        Set sh = wb2.Worksheets("Totals")
        'Set sht = Sheets("Cancellations")
        Dim LCReq As String: LCReq = sh.Cells(32, 2).Value
        Dim LCDt As String: LCDt = sh.Cells(34, 2).Value
        WbPath = ThisWorkbook.Path
        'CurDir ".."
        'CurDir ".."
        'QTPath = Left(WbPath, InStrRev(WbPath, "\") - 2)
        QTPath = ThisWorkbook.Path & "\..\" & "\..\"
Application.ScreenUpdating = False     
        If Not isFileOpen(QT) Then Workbooks.Open QTPath & "\" & QT
   
        For Each ws In wb2.Worksheets
                If ws.Name <> "Cancellations" And ws.Name <> "Totals" Then
                        With ws.[A3].CurrentRegion
                                .AutoFilter 1, LCDt
                                .AutoFilter 3, LCReq
                                .Offset(1).EntireRow.Copy sh.Range("A" & Rows.Count).End(xlUp).Offset(1)
                                .Offset(1).EntireRow.Delete
                                .AutoFilter
                        End With
                End If
        Next ws
       
'sh.Range("B32,B34").ClearContents
Application.ScreenUpdating = True
End Sub

I get the error Method intersect of object global failed and if I press debug, the following line of code is highlighted:

If Not Intersect(Target, PO) Is Nothing Then

which is within the following sub in the ThisWorkbook module

Private Sub Workbook_SheetChange(ByVal sh As Object, ByVal Target As Range)
    Dim Req As Range, PO As Range, CancelReq As Range, CancelDate As Range
   
    Select Case WorksheetFunction.Proper(sh.Name)
        Case "Totals" 'Case "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December", "Cancellations"
            Set Req = Range("B18")
            Set PO = Range("B20")
            If Not Intersect(Target, PO) Is Nothing Then
                Application.EnableEvents = False
                If PO <> "" And Req <> "" Then Call UpdateEverySheet(Req, PO)
                PO.ClearContents
                Req.ClearContents
                Application.EnableEvents = True
            End If
    End Select
End Sub

Can someone help me with this error please?

I forgot to mention, it seems to work if the workbook defined by QT in the sub LateCancel is already open but I get the error if the workbook is not open.