I have the same problem on mac os x 10.9.4
After the update to Opera v24.0 it won't open, and a pop up dialog box shows this message (it's in spanish, sorry about that):
"No se puede abrir el directorio del perfil de usuario porque careces de privilegios suficientes. Deberías llamar al administrador de esta máquina."
Wich translates vaguely to "Cannot open user data directory because you dont have enough privileges. You should call the system admin."
I'm already logged in as administrator so I'm confused.
So yes, it obviously has to do with user data. Is there any way to keep the data and make Opera work?