Since Yahoo is currently in the process of killing the remaining 100 series of SP1 and AC4 servers, Y!Epic won't log in for most users. Fortunately, there's a workaround until Y!Epic can be updated for the new servers...
On the login window, go to the Advanced Setup tab and use cs202.msg.sp1.yahoo.com as it works for me - copy and paste cs202.msg.sp1.yahoo.com into the Server: area (make sure there's no spaces before or after it!). Port nor protocol doesn't matter in this case. Match it like in this screenshot and it *should* login fine.
