I'm not sure if I've seen that one before or not. I notice you are on a really old beta version. Please try updating to the latest and let me know if the issue is resolved. Note that UI3 is out of beta now, so the URL no longer includes "/ui3beta".
Funny how that error message claims to come from the login page, when I'm quite certain I never had any version of that login page coded to load the script file mentioned later in the error message.