The so called Error 003 occurs when a System Menu, 4.2 or higher, from a different region gets installed onto a Korean Wii.
Error 003 wiis can only boot in region game disc from the recovery menu. Due to the enhanced region blocks of system menu 4.2/4.3 it is not possible to update these error 003 4.2/4.3u/j/e wiis to 4.3k, and there is no known disc with 4.3k update on it. The only way to fix a 003 error wii is to replace ios70/80 with ios60-v6174, installed into ios slot 70/80. Installing ios60-v6174 into ios slot 70/80 will remove the korean key check found in ios70/80 fixing the wii.
Currently all error 003 wiis can be fixed by loading Super Smash Bros. Brawl from the recovery menu and running Smash Stack PAL, then install ios60-v6174 into ios slot 70/80.
Do to the enhanced region checks of system menu 4.2/4.3, Super Smash Bros. Brawl can not be directly loaded from the system menu. However these region checks can be bypassed by loading an in region game disc, then swapping the disc to SSBB-pal and restarting the wii. There are a variety of methods depending on the game used, some games work, many games do not work.
All error 003 wiis 4.2/4.3u/e are 100% fixable. Disc swapping methods utilizing "Mario Kart-PWNS" and DiscSwap-PWNS" will fix the issue. Unfortunately SSBB-Pal/Kor will not load on a wii with the Japanese language setting, so SSBB can not be used as SSBB-Jap will not autoboot.
If SSBB can not be used to fix error 003, the only other solution is to load an ios used by a game that has an exploitable trucha bug present, then disc swap to an app to fix the wii using that ios.