This error shows up if the add-on does not load in 20 seconds. Because the most common reason is due to multiple accounts being logged in, I added this message. However, it does not mean that is the reason why it didn't load.
If this is only happening on one document, please share a copy with me so I can look into the issue:
je...@docvars.com
If it is happening all the time on more than one document, I may need to get more information from you to determine what the problem is. Email me directly and I will help out.
Best,
Jesse