ok have to ask this first...
says your from china and your name is catinthebox...
is that a chinese food joke ?

ok now then, looking back at your posts
you say the same thing, but no one asks you your hardware specs
nor do you offer them
so I will ask.
how are you connected to the internet? ISP,DSL,cable
going through a router or straight to modem?
what network card are you using?
have you tried another network card?
what driver version are you using?
what name of anti-virus,firewall are you using ?
what ports have you opened?
when does the "An error has occurred.Please check your network connectivity" pop up,
when you try to select a server, when you click the Multiplayer option on the main screen?
anything else you can think of that's network related
you can also dump your dxdiag.txt in here
cant promise that it will help find a solution
but you never know