Instructions
Write down the full text of the error and exactly what you were doing when it appeared. Note anything strange that may have happened to your Wii recently, like sudden battery loss in your Wiimotes or bumps to the console.
Read the manual. Basic errors and problems have answers in the troubleshooting section of the Nintendo Wii console manual.
Browse to WiiError and check your error against their catalog of errors. This independent website keeps a running list of problems with the Wii by searching through Nintendo's customer service information and through user submissions.
Use the information on the site to determine your next step. If your error isn't on the site, then continue on.
Contact WiiError and Nintendo Customer Support with the full description of your problem. If customer service responds with a solution, help other Wii owners by forwarding the solution to WiiError for inclusion in their system.