If you enable "Display invalid certificates for approval" in Options/Connect/Options/SSL, what does it show as the error in the SSL Warning dialog when you try to connect?
A window like this opens:
I click on the "OK" button and a new attempt to connect to the server starts:
*  Host disconnected
* Connect retry #2 irc.epicnet.ru (+6668)
*** Connecting to IRC chat ...
After that, all subsequent connections to the server occur without failures and errors :-]
The test was done on mIRC v7.66