I encountered this same error again (months after the earlier notice). I had installed a new update (not developmental version) to Mendeley and when I tried to add a citation from EndNote I got the “cannot edit range” message. I followed the earlier notes (some of which I had written!) and that did not resolve the problem with my citation not being formatted. I followed the steps mentioned and unchecked Mendeley as a Word Add-in and also as a Word template. When I started Word again (or maybe opened my document) I saw a status line message in the left column of Word, something to the effect that Mendeley was formatting citations. However, no citations were formatted and I had added the one citation in the document with EndNote. What worked was opening Mendeley desktop, going to the Tools menu, and uninstalling the Word plug-in. After that, adding new citations in Word worked correctly. (I think the one footnote I had added before, which was still in the temporary citation format as a footnote, was not reformatting even when I had clicked reformat citations. However, I could see a new test footnote format, so I may have deleted my original footnote and then added it back.)
I was using Windows 10 and EndNote X8.2.
I’d like to add that I DO appreciate Mendeley and use it for reading and highlighting pdfs. I like how it works for that purpose and the fact that desktop and online are both good access methods and that desktop installation on different computers synchronize with the online library very well. However, I’m more accustomed to using EndNote for citations and how it works in Word.
Have a nice day
John