In mIRC, type /ignore -rw to make sure your ignore list isn't involved, and under File > Options > DCC click the "Trusted" button and uncheck both boxes.
If that didn't help, you can use the DCC server: To listen to incoming connections, type /dccserver +sc-f on 59, then to connect to the listening machine use the command /dcc send <ip> filename. To DCC yourself, type /dcc send 127.0.0.1 filename.
(/help dcc server for details).