Jurgen Gutsch - Did you ever resolve this? Are you getting any message when you create the instance on program open? I have been struggling for years with a similar situation. I am getting the pop-up "The last time you opened ABC.xml, it caused a serious error. Do you still want to open it?" when I close and reopen VSTO WORD 16.0. It freezes my app, requiring manually clicking the "Yes" or "No". Not what we want in an unattended application.