I have a Run Time Error 91 for an Excel Add In

Question

I spent hours trying to debug this. This is a a macro to generate PDF from my selected cells. This code works on my personal workbook but when I export it as an add-in, add it in the developer tab and review the code again in the add-in workbook I keep getting an run time error 91: object variable or with block variable not set. Any help will be appreciated!

Sub Save_Selection_As_PDF_sheet()

Dim my_file As String


With ActiveSheet.PageSetup
            .LeftMargin = Application.InchesToPoints(0)
            .RightMargin = Application.InchesToPoints(0)
            .TopMargin = Application.InchesToPoints(0)
            .BottomMargin = Application.InchesToPoints(0)
            .HeaderMargin = Application.InchesToPoints(0)
            .FooterMargin = Application.InchesToPoints(0)
            '.Orientation = xlLandscape
            .Orientation = xlPortrait
            .Zoom = False
            .FitToPagesWide = 1
            .FitToPagesTall = False
            .PrintArea = Selection.Address
    Debug.Print I
    End With

FileName = ActiveWorkbook.Name
    If InStr(FileName, ".") > 0 Then
       FileName = Left(FileName, InStr(FileName, ".") - 1)
    End If
    
    my_file = "H:\data\Desktop\" & FileName & ".pdf"
    
    ActiveSheet.ExportAsFixedFormat Type:=xlTypePDF, _
    FileName:=my_file, Quality:=xlQualityStandard, _
    IncludeDocProperties:=True, IgnorePrintAreas:=False, _
    OpenAfterPublish:=True
    
End Sub