This was noted among users who have downloaded Endnote to their own laptops/MACs and the Cite While You Write function does not do what is expected..
The images named "Error image" and "Error image 2" show you an example of what has happened to other users. This occurs when you click on 'Insert Citation' in Word. Next to that button, you will notice that Word currently links to Endnote Online, where you would normally use your account details, if you have one. However, the Desktop version of Endnote does not require you to log in.
We need to change the Word settings so that it looks for Endnote Desktop
In the Endnote tab, click on 'Preferences'. In the box that appears, as shown in the image "Preferences" below, select the Application tab and in the drop-down menu select 'EndNote', rather than 'EndNote online'.