Here is what nintendo has to say.
Error Code: 86420
When does this error code appear?
Occurs Immediately: If the error code occurs immediately after selecting "With Anyone" from the Nintendo Wi-Fi Connection, our servers may be experiencing a high amount of traffic. Please try to connect again later.
Occurs when looking for a match: If the error code occurs after the matchmaking process has started, it is likely an indication of NAT Negotiation problems. Try the connection again later. However, if the error still occurs regularly after matchmaking has been running, even for more than a minute, please read the following instructions:
Do you receive this error every time the Nintendo Wi-Fi Connection attempts to find a match for you?
If you receive this error every time, please proceed to step #2 on this page.
If you receive this error only when playing a particular friend, then it is likely a problem with the friend's firewall settings on their connection. If possible, ask your friend to try the port forwarding instructions on this page.
In order to solve this problem, you may consider adjusting your router's Port Forwarding settings*. Each router is unique, so consult the owner's manual for your router or contact the manufacturer for specific information on working with your router's ports. For your information:
If you are prompted for a device or profile name, you can enter anything you like (such as Wii, etc.).
The starting port to open is 1, the ending port to open is 65535 (or as high as the router will allow).
Protocols will need to be set to UDP only.
Set the IP address for the ports to forward to the same as the Wii?s static IP address. If you don?t know what the Wii?s IP address is, the best way to determine it is by performing a manual setup:
How to manually configure the Wii?s IP address:
The first thing you'll need to do is find out what IP address range you should be using. To do this:
Click the "Start" button in the lower left-hand corner of your computer.
Next, you will need to access the command prompt. To do this:
Windows XP users click "Run."
Windows Vista users click inside the search bar.
Type "cmd" into the box and press Enter.
Type "IPCONFIG/ALL" and press Enter. The IP address, Subnet Mask, Default Gateway, and DNS servers of the PC will be displayed.
The IP address you are going to assign to the Wii must be 10 digits higher than the PC's. (e.g., 192.168.1.100 becomes 192.168.1.110). The Wii and the PC must have different IP addresses. Make note of what IP address you will assign to the Wii. Enter in the exact same values for your Subnet Mask, Default Gateway, Primary DNS and Secondary DNS. They must be the same for your Wii console and for your PC.
You will now need to manually assign this new IP address to your Wii console. For step-by-step instructions on how to do this, please click here.
After you perform the manual setup, the Wii will initiate a connection test. If the connection tests fails, then please review the values you entered. If you still cannot complete the manual setup, please give us a call at 1-800-255-3700 in the USA or Canada for assistance.
Ensure your router has the latest firmware installed. Visit your router manufacturer?s website and look for any updated firmware that may be available (these are typically found under "downloads" or by searching for your particular model number).
The error may be caused by a basic setting on the router that needs to be adjusted (such as the channel). Please review our general router troubleshooting.
If you have tried all of the steps above with no success, please call 1-800-255-3700, so that we may assist you further. Our representatives are available between 6:00 a.m. and 7:00 p.m. Pacific Time, seven days a week.
*While Nintendo provides this information for our consumers' use, it is up to each consumer to determine what security needs they have for their own networks, and to decide how best to configure their network settings to meet those needs.
