Well, I have the same problem. And this happens so often WHILE PLAYING AND WHILE I HAVE X5 !!
It's so damnit annoying. So my problem description.
e.g. I have x5 on Eu 1 New, I get kicked and when I try to rejoin, it says: This character belongs to sonebody else. Or: Somebody else is using your profilename.
I don't know why but after 2-10 rejoining tries it works as fine as before.
I don't know why I have this problem but really, it's kinda annoying. Help!
I hope I can help you if I tell you this: Try to rejoin until it works. Or also restart the game, if it diesn't help, try to repair your Launcher or whatever. If that doesn't help: Restart your computer (I don't recommend this) or wait a while.
Hope I could help you, but I also hope, that everyone (me too) gets help which really helps forever.
Greetings ;)