That dreaded error code is usually an indicator of network security issues between the two players. I've come across it all too many times when trying to play City Folk with others, myself. If you have both tried all of the suggestions provided by Nintendo's page for that error code, then unfortuantely the last resort would be to disable the firewall and security for both of your networks, which I strongly don't suggest doing. Usually though, if both parties have put their Wii within their router's DMZ and have done port forwarding correctly, there shouldn't be issues.
Do either of you have any anti-virus software that affects your network(s) at all? Try disabling that, if you're willing to, when you're trying to connect with each other.