Make sure you're using the latest and greatest. The most current version is EndNote X7.4
Get the latest update to X7 for critical updates and official compatibly with Microsoft® Windows 10. This release does not address compatibility with Microsoft® Word 2016 on Macintosh. Details
(released 11 August 2015)
In EndNote X7, under the "EndNote" menu, choose "Check for Updates".
In EndNote X7, click "Help" and choose "Check for Updates".
If you are still on an older version of X7 or want to install the X7.4 update manually, read this Knowledge Base article.