Loïc,
That looks to be an issue with how we're trying to fetch the user's avatar. In that case, the user isn't even logged in, so those PHP Notices are being thrown. Those are not actual errors, just notifications that something isn't quite right.
We'll look into fixing those. In the meantime, I'd recommend setting the Error Reporting setting in the Joomla -> Global Configuration area to "None". That will hide those notices so that they aren't showing up on your page like they are now.
I hope that helps get you started, but if you run into anything else, just let me know.
Thanks,
Alex