As you can tell, taken entirely from Mabination. Good luck!
note: it's important to not close out the client when you're switching accounts.
This is the gist of it. credit Kenero for summarizing so succintly.1. Log in
2. Go to Character Tab and try to click Rebirth.
-2a. If it doesn't work, log out and go to the character screen and then go to rebirth.
3. When Nao ask you if you want to rebirth say no.
4. Log out completely back to the Log In Screen
5. Log in
6. Rebirth
7. Fix'ed!
Basically, log into your main - try to rebirth. If it doesn't let you, log out of THAT ACCOUNT, without closing client. Then you log into another account (like a mule account) that has characters who are able to rebirth. Go into the rebirth UI for that character, log BACK OUT (without closing client), log back into your main, rebirth! Yeah, it's convoluted. ;;