empty block on page with sky theme

It seems that I have misconfigured something. Well I am searching for days now for a solution.

On everey node page I am getting an empty block with a tag.

Switching from sky to minelli fixes it. Maybe I could remove the block from /sky/templates/overrides/node.tpl.php but Iam sure this is only a bad workaround.

Thanks for your help on a beginners question