NickServ- Your nick isn't registered.
That's what it says when I try to join a server. How do I register my nickname...
Ok, I found out how to but I put the wrong email and now I can't get my passcode...what do I do?!
Nickname registration has nothing to do with mirc.
In most of them if you do not auth your nickname within 2-3 days the nickname will be dropped and you will be able to register again.
In some of them you will have to wait for about 30 days.
One solution is to find an Admin and request him to drop the nick