The so called Error 003 occurs when a System Menu, 4.2 or higher, from a different region gets installed onto a Korean Wii.
System Menu 4.2E/U/J and higher,like 4.3U. call a new ES Ioctlv(0x45) which got added in IOS70. On older(check!) IOSs this Ioctlv always returns -1017.
IOS tries to encrypt an certain byte pattern with the korean key and then compares it with hardcoded values, if the result matches it returns 0, which will then trigger the error in the System Menu.
There is currently no way known to fix this error.
Once there is a game with a 4.3K(!) update on it, one could install that via the rescue menu.