1. Are you useing the newest version of mIRC? 6.12 2. Is your mirc.ini file readonly? if so make it so its not. 3. are you sure the file being sent to you doesnt already exist (because that has a different setting) 4. after seting this feature and you go back into the setings dialog does it show your changes properly?
just a few things to check before we will be able to help you much, unless there is a known issue that i'm not aware of and someone else is.