1) This has nothing to do with the original topic.
2) This has nothing to do with mIRC.
3) This is a services problem, and it tells you quite clearly that the nick you're trying to use on that network has been registered by someone, and if you are the person that registered it, then you need to identify to the nickserv service with the password
-NickServ- This nickname is registered and protected. If it is your
-NickServ- nick, type /msg NickServ IDENTIFY password. Otherwise,
-NickServ- please choose a different nick.
If you have forgotten your password, then some networks have the ability to e-mail you your password. If you did register the nick, and nickserv doesn't have the ability to e-mail you the password, then you'll need to contact an IRCop or Admin, who can usually be found in the networks help channel (normally #help).
If you didn't register that nick, then you'll have to pick another one.