Returning Player - Can't create Character :(

[Enkidoh]

It was probably a case of that server currently was restricted simply due to having too many people logged into it at once. This can change at any time and pretty much comes down to luck of the draw sadly. SE does post regular updates on the Lodestone about the current state of servers (every six hours in fact), but again, that can change literally at a moment's notice, so that info could be out of date as soon as it's posted. But it's still a useful reference to go on to judge how congested the servers currently are.

All I can suggest is keep trying (you can save your character's appearance so you don't have to go manually through creation again and just skip straight to naming and server), and eventually you should get the server you want.

Incidentally, you could have ironically kept your original character and just levelled it two more levels, and after doing your class quests at the Thaumaturge Guild you would have been able to unlock the Armoury System which allows you to switch to any class at will by equipping it's weapon or tool. But ah well, that's something you now know for the future.