Seems your client is outdated, man! You need to update or you will put yourself on the wrong side in the world of hackers.
TBR: I think it has something to do with the update mechanism. If you don't want that warning, you need to disable updates in your login server.
Update: I checked the code, and it seems the server is sending this byte "LoginServerUpdateNeeded = 30" to the client.
What kind of server do you use? It needs to be disabled on the server side.