When I edit mirc.ini to customise various options, I save the file and when mirc is restarted the changes I made are gone. What would cause this. [ mirc 6.21, WinXP SP2, I am local admin on machine ]

make the changes AFTER you close mirc OR make them thru mirc.

NEVER change the mirc.ini file with mirc OPEN or else mirc'll take precedence over your changes.