There is already an answer on this: https://mail.ibr.cs.tu-bs.de/pipermail/ibr-dtn/2014-February/000623.html

In detail, your Pi does not support IPv6, but the daemon tries to utilize it. Calm down and check if something you expect is not working. If yes, ask again with more details. If not ignore the message.

If dtnping fails, first check if the clocks are in sync. For dtnping both clocks must not be more than 20 seconds apart.

thank you for your clear explanation :) if i can just ignore the message, my problem is still in the error ibrcommon on another subject on mailing list.

thanks johannes.