I'm pretty sure this is a fairly common one, but it baffles me it's still an issue.
I've been trying to get on all day, and yesterday I faced fairly constant disconnects, just to be met with this same message after choosing my character and reaching the loading screen.
I know it's not an issue with my internet, as every other game I play is fine and everyone in my household has had no problems.
I've also tried uninstalling the game and running a repair, but that did nothing too.
Hopefully someone can shed some light on why this is STILL a thing.