This may be one of the security barriers during this battle, no idea, lollll… Interesting, to say the least.
Still keep trying to log in. Still keep getting 51900328 error. 
Okay, I live in a rural area and I use my phone along with PdaNet+, I just tried to tether with VPN and no PdaNet, no connection; PdaNet w/o VPN, no Connection; tethered w/o PdaNet+ ormy VPN and no issues.
Blizzard you’ve got me standing here on the net naked.
Netgear routers, some have a firm ware upgrade check your router, fixed our issue where one could and one could not log in by getting the firmware upgrade.
After rebooting everything and clearing my dns on my pc still not able to login…
NM… it logged me into the wrong account and this time I finally was able to get in… until I get the World Down error.
I finally managed to log into my character! Thank you!
Been waiting for a few hours for them to address why some people cant log in and why others can. All we are getting is silence. Terrible service. Has it always been like this? Would expect more from such a wealth generating product.
Now I’m stuck on the path between blasted lands and swamp of sorrows. Cant go anywhere, it says Transfer Aborted: Instance not found. Even tried hearthing same thing 
Sometimes it just takes looking around a little bit Sprinkels. Your post was merged into this one where there’s been ongoing communication/troubleshooting from blizzard for quite some time.
Still can’t log in. (WOW51900328).
Ok that was short lived. I had to force exit the game because my character kept getting instance not found spam, and now I cannot log in again.
Wyrmrest appears to be down? I was in the middle of dailies and suddenly it looked like I was lagging out. Restarted the game because it was basically frozen and now it’s stuck on trying to connect to game servers.
now its world server down on westfall server again. thats how this started last time hehe
Herod seems like down again.
i was briefly able to play after restarting my router, but soon was disconnected and getting the error again
world server down for whitemane
Herod is down. I can login to the character select screen but then when I try to load any character it just hangs at about 80% and then after about 1-2 minutes I get DCed. Herod is listed a High population so I don’t know if that is just a bunch of people at character select screen or if anyone is actually in the server.
Kul Tiras Realm some friends are online and active on this realm but I cannot connect to the server. 328 and 319 errors
I kept getting WOW51900328. Can’t log into any realms.
Tried for the whole afternoon, what a waste of time!
I’m done.
Same here I give up WOW51900328 error maybe it will be fixed tomorrow but somehow I have my doubts.