The so called Error 003 occurs when a Korean Wii gets region switched to a different region and then updated to 4.2 via the online update.
System menu 4.2x calls a new ES Ioctlv(0x45) which got added in IOS70 on other IOS' this Ioctlv always returns -1017.
If the korean-common-key is present IOS70 will return 0, which will then trigger the error in the system menu.
Since the rescue menu still works you can use it to fix your Wii, you also need a drivechip or any other device making your Wii capable to play burned discs.
Get one of the games which load the exploit from SD (ie. SSBB or Indiana Pwns(?)). Create an autoboot disc from it and use it to run i.e. a wad installer to install a different system menu or a tool which patches the check out.