90002 isn't a network error, it's a client error.

I had the same problem for a long time and what I discovered was that my CPU was actually missing a cycle every now and then which threw off my system clock by fractions of a second. Apparently that's enough for the client to 90002 you because it thinks you're speed hacking or something, I don't know what it thinks it's doing. The FFXIV client is SUPER paranoid about any kind of system clock issues. The way to test for this is to try the game on a different computer on the same network.