Read this article for things you can check if you find that EndNote and Word won't play nicely together, and ways to fix this.
Microsoft Office latest news (updated July 2016):
EndNote X7 for Windows is compatible with Word 2013 and 2016.
For more on software compatibility, look at this article.
If you are having trouble with Cite While You Write in Mac OS 10.8.2, look at this article.
If you use EndNote with Pages, look at this article.