Acceptance box: Position error message

Hi,
I have a problem with the position of the error message.
If you try to send the form without accepting the “Datenschutz”-Box you got an error message. But the message destroys the layout. It shout appear above or under the the text: “Ich bin mit der Erhebung und Speicherung meiner eingegebenen Daten zur Kontaktaufnahme einverstanden.”

In fact it appears somewhere in the middle.
Have you any ideas how to solve this problem?

Thanks!!

The page I need help with: [log in to see the link]