How to join an old world?

[fo6h05mn2w]

Is it possible to join old worlds still? 

World 25, for example, is quite old. It seems there are open spots for new players. But there is no way for a new user to join!

[raidnow]

Why Can't I join an old world AGAIN? I have an account in Wrath 17.... But now I can't open Wrath 17 server... But I still can open my account in Tiberium Alliances. It says: You cannot start in this sector. WHY???? Please help me.....