Hi.
As many of you know, something like this pop on your screen whenever you have that problem:
(https://i.imgur.com/mwdSrzY.png)
What are the reasons that cause this problem?-The user has picked up an improper nick name.
-There is already an online player on the server with the same nick name that the player has chosen.
-A client-sided bug caused by unstable connection.
Ensure you are not using any disallowed characters in your name (use 0-9, a-z, [], (), $, @, ., _ and = only), and your name is no longer than 20 characters. This also could be caused when a player is on a server with the same name as you (which can happen if you re-join a server very soon after timing out or crashing). Also a Windows server running SA-MP with a uptime greater than 50 days can cause this bug.
This bug is mostly caused by the same reason as "You are banned from this server bug". The player has got a nick-name that meets the server requirements however a notification text shows up, saying that the nick-name is improper.SUMMARY
-Wait for a while before reconnecting.
-Re-install SAMP, delete "gta_sa.set".