Problem with nickname

[Nguyen_Baro]

How can I fix the problem of unacceptable nickname, i change my nickname which suit with the commands, but i still get a trouble with it, pls help me

[BlackyBurn]

This error usually appears if you're using a Nickname with unacceptable characters or if your username is already logged into the server.
It can also happen if your game just crashed and you try to reconnect, if that's the case, give it a couple of good 10 seconds or so and try logging in after.
If you're using unacceptable characters, delete them and try logging in again.

[mind]

How can I fix the problem of unacceptable nickname, i change my nickname which suit with the commands, but i still get a trouble with it, pls help me

You can also try change IP, maybe could work.