Finally I've solved my own "cannot DCC send" problem! Since I installed a wireless router I wasn't able to send or receive files. I tried rerouting ports in the router and lots of other things, but nothing worked. Finally I solved it in this way:
- I removed all port rerouting from router
- In mIRC options "Connect .. Local Info" I checked Local Host and Normal Lookup Method
- When sending I always use Passive DCC on
I hope this is useful for other people too.