I had a similar issue. I’m running a Mac, and upgraded Word to Word 2016. When I tried to format citations in Word 2011 (which I am keeping because Endnote hasn’t yet created an update that is compatible with 2016), I got the the dread “1701” error. I think I have a solution, though: go to the Endnote X7 menu (top left), click on “Customizer,” and reinstall the components that appear in the dialog box. (You need to make sure that Word is not running when you do this.)
No guarantees, of course – but it did resolve the problem for me.
Good luck!