Failed to connect to instance.

When I click "Log in" all is fine, it takes me to the character selection screen.
Then it proceeds to load for a bit and then I am taken back to the main menu and a message is show, "DISCONNECTED - Failed to connect to instance".
I played another game to see whether my internet connection was the problem and it seems like my internet is not the issue since I was getting a stable internet connection on that game. What should I do? Please let me know.
I was in "The Glade" when I was last playing the game.
Please fix this as soon as possible.