Hmmm, if the error message is correct then it pertains to 6to4 which has not much to do with SixXS, except for it being an IPv6 transition technology. See the Wikipedia article on 6to4 for details on what it is. What the error says though is that you have a private IP address, thus something in RFC1918 address space, eg something in 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. Due to the way 6to4 works, it embeds the IPv4 address inside the IPv4 address, this cannot be used for 6to4. As you are apparently behind a NAT you have four options for resolving this issue: 1) Let the Fritz!Box do the NAT function instead of the device that does it now. 2) Use AYIYA through a SixXS tunnel. 3) Use TSP through Freenet6 4) Use Teredo for a single host