Check for an ip mismatch by typing /dns yournickhere and then typing //say $ip and compare the two. If they arent the same, type /localinfo -u and then try to DCC send.
Thanks A LOT. This just paragraph solved almost 3 years of ignorance and 'messing stuff up'.
Really, thank you a lot. I think this should be included in mIRC's options (somehow). Thanks again for your great support.