I now have this problem. Or at least one very similar. I can connect to some servers trouble free and ther servers I get "Lost Connection to host" within seconds of joining.
There is one particular server that I play alot on and have always been able to connect, have good ping and untill yesterday never lost connection.
I have connected to this server many times trouble free with patch Z. I am not banned in any way from the server - quite simply something has changed. I have checked ports & firewall and all is fine, the only thing I can think of is that I did some file maint on my PC at the weekend.
Not sure if its relevant but this included cleaning browsing history, saved passwords etc.
Doubt its got anything to do with it but im outta ideas.