When starting a Wii game, I get this message on a blue screen:
An error has occurred. Press the Eject Button, remove the Game Disc, and turn off the power to the console. Please read the Wii Operations Manual for further instructions."
Turning the console on and off doesn't help. What's going on and how do I get my game to play?
This error most often effects homebrewed Wiis. If you do not have homebrew installed on your Wii, and have not hacked it in any way, then you might have luck doing a system update. If that doesn't work, you'll probably want to contact Nintendo support.
If you have homebrew installed on your Wii, then this is probably an IOS problem. The IOS is the part of the operating system that loads games, and different games use different IOSes. In a non-homebrewed Wii, the game will install the proper IOS if it isn't already there, but operating system updates from Nintendo are designed to destroy homebrew, so homebrew users avoid updating.
In some cases you can simply run a game using the homebrew application Gecko OS, but there are also programs that will install the necessary IOS. Wad Manager is a popular one, but I used Pimp My Wii. (Note: the website that hosts these files adds updates to them as separate files, so my links may not link to the latest version. Your best bet is to simply search the website's download section.)
Pimp My Wii will optionally automatically install all IOSes and non-homebrew-breaking updates, but you can also choose which updates you want, which is the more cautious approach, and the one I took. If you want to select only the IOS you need for a particular game that won't run, check this list which shows which IOS is used by each game. Once you know what IOS you need, choose each IOS in the Pimp My Wii interface and the program will download and install the appropriate files. At this point your game should play. (I assume Wad Manager works in a similar way, but I haven't tried it.)
Note: When I ran Pimp My Wii I installed a few additional updates besides the necessary IOSes. One of these updates re-enabled update checking, which I had turned off. So after running an update program, be aware that you may, depending on what you update, have to re-disable update checking.