This is very seriously bug as you never fixed in SL. Come on?
There are some things you can get that bug.
When I arrived Night Fae area and then I jump down from where floghtmaster is, disconnected insant. Restart wow, loading character and diconnected insant. FIX IT so it wont happen again.
51900319 is actually a very generic bug that has multiple possible causes.
It basically means “Something went wrong!”
Bugs are reported in-game not via the forums, btw.
You cant report in-game due to disconnected. 
I have the same issue…arrive at the night fae area…jump down from the flightmaster i get disconnected…cant play this character because of the insta disconnect…and cant report ingame because of that…how can i fix this
I had to wait few mins before I could log without disconnected. Not only this happens, you can get disconnected when you land with goblin glider in Bastion.
I have same problem-Error 51900319
I get this error everytime i log out to my character selection screen, no problem loging back in tho. Been like this for a while now.
i get the game Error what can we do about it ?
They need to fix bug or smt.
Getting it right now when I try log in to any char that is in revendreth.
As I did WB on all chars then loged off to do RL stuff and now back to game, it means all chars are stuck in an endless loop of 51900319.
Feels bad, man.