Good afternoon and thank you for posting on the Final Fantasy XIV Technical Support Forums.

Did you disconnect from the game while playing the instance, or was it while you were in a loading screen?

Usually, this kind of error can resolve itself. In case this doesn't happen, try the following:

Check the following Port Ranges on your router/modem to ensure that they have been opened:
▼TCP
54992 through 54994,
55006 through 55007,
55021 through 55040
Your ISP can open these ports for you.

We hope we can be of assistance in helping you enjoy the exciting world of Final Fantasy XIV!