Owo ti je sa jednog drugog foruma. Pa ako razumiješ engleski nije ti problemLAN games restricted to class C
This basically means you are trying to join a LAN server, a server where you need to be on the same network in order to play. So if you are trying to join over the internet then you can't.
If you are trying to set up a server and players can't join because they are getting this error, then you need to type sv_lan 0 into console on the server side, or add in to the server config file.
One final posibility is that you are using a cracked/hacked version of Steam - if you get this error on all servers then this is quite likely to be the cause. If this is the case, u could get the official version of Steam, buy a copy of a game then register the cd key and dont be so cheap.
Maybe the server you want to join has a different version of yours.