re settings prob:
Go into your windows explorer, find the directory you have mIRC in, and right click on mirc.ini. choose properties, and make sure you dont have the box checked for "read only".
re dcc:
If by "software error" you mean you get disconnected with "software causes connection abort" error 10053 during dccs, thats seems to be rather common especially for winXP users. Doesnt seem to be a one answer fits all for it. Some:
-connect to the networks server on a diff port than 6667
-check your router firmware/drivers
-dont use speed patches
-disable xp's firewall
You can use the search feature here, all forums, all posts with 10053 as search term to read more especially if you are using xp. Theres a description of that error in the connection problem area here under "common irc errors"