A 90000 error means the connection between you and the server was interrupted. Unless everyone on the server is kicked it almost certainly means it's a problem with your ISP/the route to the server. Metrics such as "i just finished downloading the game" are not accurate, even with a very high rate of packet loss a file can be downloaded.

It's also very possible that your connection to most/all other sites that you use are fine while the connection to SE is not, despite the problem not being on SEs end. If you're both in the US it's more than likely you're both experiencing issues with a bad router currently owned by Level3. It's part of one of the main routes between the US and Canada (where SE hosts FFXIV:ARR) for most ISPs and has been misbehaving itself for several weeks now.