These may be the problems that may help you solve it! MORE IDEAS MORE BETTER! :3
Error Code: 86420
This error occurs when there is a communication problem between players during online gameplay.
Try this:
If your router's security software (firewall) is turned on, it may block communication that is required for online gameplay. To fix this, try disabling the router's firewall*.
Most firewall settings are located under the "Advanced" or "Security" tab.
If the problem still persists with the firewall off, you may need to open ports on your router through the Port Forwarding feature.
Create a manual connection on your Nintendo DS and assign a static IP Address.
Open ports 1 through 65535 as both TCP and UDP.
Ensure the ports are forwarded to the same IP Address given to the Nintendo DS system during the manual setup.
Trouble connecting to a friend?
If the above steps have not resolved the issue and you are trying to connect with specific friends, the problem could potentially be an issue on your friend's network. Your friend will have to perform these troubleshooting steps with their home network.
Using USB Connector or Lan Adapter? Please call 1-800-255-3700 so that we can assist you further. <--- Number to dial if you cannot understand yet of the problem or it no work D;