I’m guessing this problem hasn’t been fixed yet, but I might have found a workaround. It seems this problem is caused by the travelling library in the word file. I’ve been able to silence the error message by clicking the Endnote menu in Word and then re-exporting the traveling library to an Endnote file. In my case, I just export to the same Endnote file every time I open my paper either with or w/out Endnote actually running. This seems to shut it up, at least until the next time the document is opened.