At random times our clients have reported getting a message indicating “Error 520” when they attempt to log into the website. This sort of error can be caused by cookies or other programs which have become attached to your browser over time.
The best way to alleviate this sort of issue is to clear the cache and cookies from the browser that you are using. Please see the following links to learn how to accomplish this with some of the more popular browsers:
Clearing the cache for Firefox
Clearing the cache for Google Chrome