The reverse DNS stuff is just extra info.
The fact that you are getting the same error (please stick to error messages returned by plain mIRC), suggests to me your firewall is blocking your connection. This can be the cause of a recent (firewall) update or the installation of a new mIRC version.
Try to remove any exception for mIRC from your firewall settings and then re-add mIRC as a firewall exception.
Can you connect to other IRC networks or does the problem only occur with SwiftIRC?
