It's most likely some sort of port issue. I highly doubt it's mIRC's fault specifically, but rather your router setup. I recommend contacting the router manufacturer and trying to sort it out with them. If possible/feasible, try disconnecting the router and then DCCing, to ensure it's the router causing the issue.
The router technical assistants will probably have a better (and more technical) idea of what it could be. Search their website too and see if they have some sort of knowledge database, they're always good.
Just an FYI, typing in caps is considered shouting. Whilst these problems can be extremely frustrating (we've all had 'em at some point!) you will get the same answer with 'HELP ME NOW' as you will with 'help me please
Best of luck, hope it gets sorted. Might want to click the little fnger icon in your last post to receive email notification when someone replies to your post, incase others post their ideas of what it could be...