Owncloud forbidden?

My owncloud installation gives me the message that it doesnt have a working internet connection. As I read through some posts i found out that it is trying to connect to owncloud.org.
As i tried out to open the site in chrome this error appeared to me:

I tried out on my mobile device which isnt connected to the local wifi and there the site works.
Whats happened?

I had the same issue, looks like their IPv6 configuration is broken. Works fine on IPv4, try that if you can.

How can I do that??_