Your main domain name is redirecting some error message image on Dropbox. It's just an image on an HTML page, rather than a real error. Then, there's a script that redirects you to your addon domain after several seconds.
Check your main domain's files for a redirect.
As a reminder, make sure you provide a full manual translation of your website to English, Spanish, or French as soon as possible to avoid being suspended for breaking the language rule of our TOS.