just logged out to switch to another character and got booted out by error 5006. now I get it every time after entering password and clicking Play, if the Data center I select is Aether (I'm from Balmung). Swapping to a japanese datacenter (Gaia, I have an alt on Zeromus) didn't give me any issue.

Edit: After logging in the Japanese server and going back out to the main menu, I was able to access the Aether data center and then log on Balmung successfully.