Make sure your Microsoft word version is compatible with EndNote version. I have Microsoft word 2010 32 bit version and EndNote X6. Remember there is a problem with word 2010 64 bit which is not supported by EndNote. I'm not sure it is currently resolved or not but if thats the case this solution will not work.
You can check your word version by going to the File>Help where you can see the Office version.
Now here's how to enable the EndNote Add-Ins.
- Click "File" then click on "Options"
- Click "Add-Ins" from the list
- Select "COM Add-Ins" from the drop down list next to Manage at the bottom of this Add-Ins and then click "Go" button
- Now you can see the EndNote Add-In in the given list and make sure that Add-in is checked.