according to the gamesnet website, there are other servers you can try, http://www.gamesnet.net/servers.php
to turn off remotes (scripts) in any window of mIRC, type /remote off
as for "replying to pingpong" yes, you did reply, sounds like you had it hidden before in mIRC's options. The ping is the server pinging you, the pong is mIRC's response to it. If the time between is too long, then the server decides you are amongst the missing and "ping times you out", disconnects you.
I would just be guessing what they mean by client, as they could mean either one. Have you tried posting this on the gamesnet forum? they would be more familiar with how things work on gamesnet than many of us are. http://forums.gamesnet.net/