I've been trying to track down this problem for a few days down, and my best guess is that this is server load related. I went through the whole ordeal of swapping drivers and reinstall. I'm pretty convinced the error doesn't lie with me. My event log cites ffxigame.exe as the culprit. During peak times it appears that Ul'dah is "at capacity", and as a result I'm unable to go there, or login if I had logged there previously. If I wait until an off-peak time I see that I'm able to run into Ul'dah no problems.

I was wondering with the increase of people returning soon is there any effort to do some more load balancing of some kind to help with the influx of traffic through Ul'dah.