Type /sreq auto
However, if you're receiving a "cannot connect" error, it seems you're having a DCC problem. The problem is usually at the sender's end, so ask a couple of friends to try and send to you. If that works, then it's not your end that's the problem. If you can't DCC get though then see http://www.mirc.co.uk/help/getproblems.html
- the most common problems with DCCs are firewalls/routers.
Also, don't forget that mIRC is not a file trading program