Make sure you're using the latest and greatest. The most current version is EndNote X7.2.1.
The latest release for EndNote X7 lets you share your entire library – references, PDFs, attachments, and all – with up to 14 other EndNote X7 users, no matter where they are located. Plus, with unlimited online storage you can store and share as many files as you need.
To start sharing a library, just install the update, open the EndNote desktop, and select File > Share.
(released 11 December 2014)
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 (X7.0, X7.0.1, X7.0.2, X7.1) or want to install the X7.2.1 update manually, read this Knowledge Base article.