http://forum.square-enix.com/ffxiv/t...17#post2162917 reason posted here:

[NA] All Worlds Emergency Maintenance (Jun. 5)
At the following time, in order to address login difficulty issues, we will be performing emergency maintenance on all Worlds. During this period, FINAL FANTASY XIV: A Realm Reborn will be unavailable.

We apologize for any inconvenience this may cause and thank you for your understanding.

* The World transfer service will be suspended, and will be unavailable until maintenance has ended.

[Date & Time]
Jun. 5, 2014 from 5:25 a.m. to 7:00 a.m. (PDT)

* The completion time may be subject to change.

[Affected Service]
- FINAL FANTASY XIV: A Realm Reborn