I can confirm this issue with mIRC 7.15. The only option necessary to reproduce is: Tools -> Options -> Connect -> Options -> Ports... -> "Bind to Adapter or IP address".
Enter a valid local IP address or choose an adapter. After that a reconnect to previous reachable servers is not possible anymore.
The only message in server window says: Send error ([10054] Connection reset by peer).
Uncheck that option and (mostly) everything is fine. Establishing a DCC chat is not possible anymore without that option.
Greetz.
