Cann't connect to Facebook Latest version.

After step 2.1 (manual) "Select a page" --> [Continue], we get "Internal Server Error". The url is:
http://messinia.net.gr/administrator/index.php?option=com_socialbacklinks&view=plugin&task=networkConnect&network=facebook&tmpl=component
or
http://messinia.net.gr/administrator/index.php?option=com_socialbacklinks&view=plugin&task=networkConnect&network=facebook&callback=1&tmpl=component&bundle=eyJh.....n0=

We also have installed K2. We config both facebook buttons but none of them works.
Twitter and Linkedin work fine.
What should we do?
Please, answer us as soon as possible.
Thank you in advance.