That error code is still one from before connecting to the server, so it is still an issue on your end.
Are you sure that everything you put in for your connection settings is correct? Is the wire securely connected both on your Gamecube and on your router/switch (i.e, when you try to connect, does the light for whatever port your Gamecube is connected to light up properly)?
Everything I put in was correct, and everything was connected properly. But I now found out what the mistake was, and fixed it!
My Ethernet extender seems to have been dis-linked from the main router, due to a long period of inactivity. (If you don't use it for a while, you'll have to re-link it again) That's why I was unable to connect after solving the IP issues.
Everything is fully functional now!
Thank you, everyone! You too, elfangor, as it was pretty helpful to a certain extent!
I am finally online! Oh my god!