Seriously man, all I can tell you is that this is a complete mystery.

I first got the game about 4 or 5 days ago. The first day, I could not play at all because I received nothing but error 90000 and error 2002 messages. I was starting to think it may be my poor internet connection (seriously, its not the best around), but I then managed to get online with absolutely no issues for 2 days straight.

Now here I am again, today, and I have not been able to log in a single time. I bought the game on a maintenance day, so I'm wondering if there's some sort of strange connection to server issues and maintenance (there was some performed recently).

It's really strange how this is happening... I even sent in a ticket about the error messages, and I got the same cut-and-paste reply many others received. Something to the effect of, "the error messages are simply caused by server congestion and try again later." I definitely agree with the "try again later" bit. That seems to be the only method there is right now.
I'll tell you right now, its probably not a problem with your internet. SE just has some work to do.

Its a bummer... this game is great, but almost not worth the trouble.