Manuel,
Sorry for the issue. The problem will be fixed in the 6.2.2 release, due out later today.
One quick fix is to go to the JFBConnect -> Social -> Misc area and set the "Admin Render Key" value to anything, like "hi". That should fix that module right away, but if you have implemented any Easy Tags on your own {SCOpenGraph} or {JFBCLike} etc, you'd need to update those with the key you set.
I hope that helps explain and get you going. If not, or you have any other questions, just let me know.
Thanks,
Alex