Just saw this bulletin:

We are currently experiencing technical difficulties wherein players on certain ISPs are occasionally unable to log into the North American/European data center Worlds on FINAL FANTASY XIV: A Realm Reborn. The issue is being addressed, and new updates will follow as additional information becomes available.

We apologize for any inconvenience this may cause.

[Date & Time]
From Feb. 19, 2014 7:10 a.m. (PST)

[Details]
Players on certain ISPs are occasionally unable to log into the North American/European data center Worlds.

[Affected World]
- Adamantoise
- Balmung
- Behemoth
- Brynhildr
- Cactuar
- Cerberus
- Coeurl
- Diabolos
- Excalibur
- Exodus
- Faerie
- Famfrit
- Gilgamesh
- Goblin
- Hyperion
- Lamia
- Leviathan
- Lich
- Malboro
- Mateus
- Midgardsormr
- Moogle
- Odin
- Phoenix
- Ragnarok
- Sargatanas
- Shiva
- Siren
- Ultros
- Zalera