Cannot do this simple task

I'm trying to append a text in a file text but error 5 popups, here's my code

Option Explicit
Sub Appentext()
Const ForReading = 1, ForWriting = 2, ForAppending = 3
    Dim fs, f
    Set fs = CreateObject("Scripting.FileSystemObject")
    Set f = fs.OpenTextFile(ActiveWorkbook.Path & "\pool1.txt", ForAppending, TristateUseDefault)
    f.Write "Hello world!"
    f.Close
End Sub

I referenced the module to Microsoft Scripting Runtime. I use Excel 2016.
I do not know what is happening,