Prevent save unless all cells or certain cells are filled in

Try

Private Sub Workbook_BeforeSave(ByVal SaveAsUI As Boolean, Cancel As Boolean)
    If WorksheetFunction.CountA(Sheets("Sheet1").Range("B5,C9")) < 2 Then
    Cancel = True
    Msg = MsgBox("Please complete cell B5 and C9 to continue ", vbOKOnly)
Else
    If WorksheetFunction.CountA(Sheets("Sheet1").Range("B5,C9")) = 2 Then
    Cancel = False
    End If
End If
End Sub

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