You can try to delete a registry key located at: HKEY_CURRENT_USER\Software\Microsoft\VSTA\Solutions\{GUID} The value of {GUID} will be different on your environment. Check to ensure that you’re deleting the right key. Confirm by checking the DWORD “Url” value at the key. Restart Excel and you should be good to go.
Pandoc supports conversion from docx to markdown directly: pandoc -f docx -t markdown foo.docx -o foo.markdown Several markdown formats are supported: -t gfm (GitHub-Flavored Markdown) -t markdown_mmd (MultiMarkdown) -t markdown (pandoc’s extended Markdown) -t markdown_strict (original unextended Markdown) -t markdown_phpextra (PHP Markdown Extra) -t commonmark (CommonMark Markdown)
Microsoft has a kb article (link currently broken, Internet Archive snapshot) that covers Protocol Discovery in fine detail. Essentially, Office is trying to determine if your server supports WebDAV (or something like it) so that changes the user makes to the Office document can be pushed back directly to the server.