If Strider is getting refusal from the server for the reason he quoted then either HOP is an IRC command where he chats or his script is using HOP as an alias for a command he doesn't have access to, I was just helping him rule out the first bit. He'll have to check his aliases otherwise.
Note this comment from KingTomato which is correct: hop is to rejoin a channel that ur presently in.
Your note that on some IRCd's the key is sent as a part message, all I can say to that is that it comes down to sloppy IRCd coding as I cannot see the key being actually sent by mIRC in the @Raw window.
