You are probably trying to place them in Program Files, which is no longer used since WinVista. You need the mIRC directory under Application Data.
Type //run $mircdir in mIRC to open the dir that contains settings files.
Thank you for your reply, it is greatly appreciated! You are correct, I placed the new IRC in Program Files (x86). I'm not totally following your next step though. So I just need to move my new IRC folder to the 'Application Data' folder and then copying & pasting the old mIRC.ini file to the new mIRC.ini file?
Thanks again for the reply.