Changing name servers on GoDaddy causes error

On de.godaddy.com I tried changing the DNS records of my domain (it-wiz.de) to:

[ ] ns1.dynv6.com
[ ] ns2.dynv6.com
[ ] ns3.dynv6.com

This fails with the following reason:

InvalidNameserEntry

Any idea why?

Thank you.

I have the same problem (with some different name servers from another dyn dns service)
Would also appreciate help!