When i'm trying to log in my own server, i have this issue :

Internal Exception : java.io.IOException: Received string length longer than maximum allowed (20 > 16)

On the Dirt background.

I haven't any mod, bought the game, and my nickname is 5 letters, and a number. I've tried to log in another server, and it was done successfully.

In the server log, it's typed :
INFO Pseudo Insert my ip here logged in with entity id 11 at (-200.70592908671622, 55.11396569842837, 2.526654128268823)
INFO §6Pseudo§r joined the game
SEVERE Reached end of stream for Insert my ip here
INFO Pseudo lost connection: disconnect.endOfStream
INFO §6Pseudo§r left the game

I don't know why there are those §6 and §r next to my nickname, is it the problem ? My server is 1.6.1 updated too.