I'm really sorry, Fix, i really don't want to be a nuisance...from where the hell you even have this metroid code? seriously man why are you surprised that you cant get codes to work if they arent even listed somewhere? I googled the code you gave me there and it appears to be the first half of some infinite life cheat?
I got the metroid Prime codes from geckocodes...
https://www.geckocodes.org/index.php?c=GM8E01
Forgive my lack of knowlege, I didnt knew about the clash of codes.
And you are right all the way to the end: I just used ONE gct file with ONE code ( infinite energy ) on Luigi's Mansion, and it WORKED... In my case, that's all I need for any game.
Pikmin was crashing during gameplay, I created a gct file with one code for it, and it goes fine now.
Metroid really didn't had any effect. I believe the code is really incomplete, because in the link above, there's only two mastercodes, so, I think it's a code to activate another code... That doesn't exist there. So I can choose one of them, but if there's no code to mastercode activate, no code will be active.
Is that it? I really don't know, again, sorry for bothering all of you guys with this issue...