sv_lan 0 maybe?
"lan servers are restricted to local clients (class c)" shows up when i create a newgame server and my friends try to join. The server is only for lan then. just type sv_lan 0 in server.cfg or something.
you said that you had a dedicated server... when you are starting it that little window will pop up with settings about servername, map ect. maybe you have "lan" instead of "internet" in the settings there...
+karma if helped
