You need to open a few tcp ports in your firewall and router. The 1031-1050 range should be plenty, then configure mIRC to use those same ports for DCC...
options (alt+o) > connect > options > advanced button
Select 'DCC' .. de-select 'Other'
First: 1031
Last: 1050
Select 'Randomize ports' or 'Use random ports'
If you're unable to open these ports in your firewall and router, then just delete the file you're trying to resume and start over.
