There is nothing in the code you posted to tell Word where to look. If it's not finding the file now, I doubt it would have found it before. Furthermore, it can't look in the current document's folder until that document has been saved; until then the document doesn't have a folder to look in! You should add the full path to the document or, if you can be sure the document has already been saved:
.InsertFile FileName:=ActiveDocument.Path & "\Tabellmall Standard.docm", Range:="", ConfirmConversions:=False, Link:=False, Attachment:=False