When you can get on other networks/servers but not one in particular, logically that indicates the problem is with that network/server. It isnt uncommon for networks/servers to have problems and be hard or impossible to get on for a period of time. Since several ppl have reported the exact same problem over the past few days with mircx, i'd check on their website for any info about it.
mIRC isnt connected with the administration of any network, so we cant know whats going on behind the scenes any more than you can.
