Go into the mIRC options to the Local Info section and make sure you set it to what you see in the pic below:

 [img:1crx467n]http&#58;//www&#46;luniz&#46;org/images/irc/mirc-local_info&#46;jpg[/img:1crx467n]

Then go to the DCC/Options section and set a range of DCC ports to use for DCC sends, as you see in the pic below:

 [img:1crx467n]http&#58;//www&#46;luniz&#46;org/images/irc/mirc-dcc&#46;jpg[/img:1crx467n]

Now, if you have a router, you will need to open (port forwarding) this range of ports to your LAN ip.  Also note to use a range of ports that something else isnt going to be using.  That is why I use 2500-5000.  But you dont need to use such a large range, but enough to be able to send more than 1 dcc at a time.  Once you set these options up, you should not have any problems with DCC sends.